Basics java scripts

Java Script
Introduction

JavaScript is a programming language that can be included on web pages to make them more
interactive. You can use it to check or modify the contents of forms, change images, open new windows
and write dynamic page content. You can even use it with CSS to make DHTML (Dynamic Hyper Text
Markup Language). This allows you to make parts of your web pages appear or disappear or move around
on the page. JavaScript’s only execute on the page(s) that are on your browser window at any set time.
When the user stops viewing that page, any scripts that were running on it are immediately stopped. The
only exception is a cookie, which can be used by many pages to pass information between them, even
after the pages have been closed.

JavaScript has nothing to do with Java. JavaScript, originally nicknamed Livewire and then Live
Script when it was created by Netscape, should in fact be called ECMAscript as it was renamed when
Netscape passed it to the ECMA for standardization.

JavaScript is a client side, interpreted, object oriented, high level scripting language, while Java is
a client side, compiled, object oriented high level language. Now after that mouthful, here's what it
means.

Client side
Programs are passed to the computer that the browser is on, and that computer runs them. The
alternative is server side, where the program is run on the server and only the results are passed to the
computer that the browser is on. Examples of this would be PHP, Perl, ASP, JSP etc.
Interpreted
The program is passed as source code with all the programming language visible. It is then
converted into machine code as it is being used. Compiled languages are converted into machine code
first then passed around, so you never get to see the original programming language. Java is actually dual
half compiled, meaning it is half compiled (to 'byte code') before it is passed, then executed in a virtual
machine which converts it to fully compiled code just before use, in order to execute it on the computer's
processor. Interpreted languages are generally less fussy about syntax and if you have made mistakes in a
part they never use, the mistake usually will not cause you any problems.

Scripting
This is a little harder to define. Scripting languages are often used for performing repetitive tasks.
Although they may be complete programming languages, they do not usually go into the depths of
complex programs, such as thread and memory management. They may use another program to do the
work and simply tell it what to do. They often do not create their own user interfaces, and instead will
rely on the other programs to create an interface for them. This is quite accurate for JavaScript. We do not
have to tell the browser exactly what to put on the screen for every pixel, we just tell it that we want it to
change the document, and it does it. The browser will also take care of the memory management and
thread management, leaving JavaScript free to get on with the things it wants to do.
High level
Written in words that are as close to english as possible. The contrast would be with assembly
code, where each command can be directly translated into machine code.
What is JavaScript?
• JavaScript was designed to add interactivity to HTML pages
• JavaScript is a scripting language

• A scripting language is a lightweight programming language

• JavaScript is usually embedded directly into HTML pages

• JavaScript is an interpreted language (means that scripts execute without preliminary
compilation)

• Everyone can use JavaScript without purchasing a license

Are Java and JavaScript the same?

NO!

Java and JavaScript are two completely different languages in both concept and design!

Java (developed by Sun Microsystems) is a powerful and much more complex programming language - in
the same category as C and C++.

How is JavaScript constructed

The basic part of a script is a variable, literal or object. A variable is a word that represents a
piece of text, a number, a boolean true or false value or an object. A literal is the actual number or piece
of text or boolean value that the variable represents. An object is a collection of variables held together by
a parent variable, or a document component.

The next most important part of a script is an operator. Operators assign literal values to variables
or say what type of tests to perform.

The next most important part of a script is a control structure. Control structures say what scripts
should be run if a test is satisfied.

Functions collect control structures, actions and assignments together and can be told to run those
pieces of script as and when necessary.

The most obvious parts of a script are the actions it performs. Some of these are done with
operators but most are done using methods. Methods are a special kind of function and may do things like
submitting forms, writing pages or displaying messages.

Events can be used to detect actions, usually created by the user, such as moving or clicking the
mouse, pressing a key or resetting a form. When triggered, events can be used to run functions.

Lastly and not quite so obvious is referencing. This is about working out what to write to access
the contents of objects or even the objects themselves.

As an example, think of the following situation. A person clicks a submit button on a form. When
they click the button, we want to check if they have filled out their name in a text box and if they have,
we want to submit the form. So, we tell the form to detect the submit event. When the event is triggered,
we tell it to run the function that holds together the tests and actions. The function contains a control
structure that uses a comparison operator to test the text box to see that it is not empty. Of course we have
to work out how to reference the text box first. The text box is an object. One of the variables it holds is
the text that is written in the text box. The text written in it is a literal. If the text box is not empty, a
method is used that submits the form.

What can a JavaScript do?
• JavaScript gives HTML designers a programming tool - HTML authors are normally not
programmers, but JavaScript is a scripting language with a very simple syntax! Almost anyone
can put small "snippets" of code into their HTML pages
• JavaScript can put dynamic text into an HTML page - A JavaScript statement like this:
document.write("<h1>" + name + "</h1>") can write a variable text into an HTML page

• JavaScript can react to events - A JavaScript can be set to execute when something happens,
like when a page has finished loading or when a user clicks on an HTML element

• JavaScript can read and write HTML elements - A JavaScript can read and change the content
of an HTML element

• JavaScript can be used to validate data - A JavaScript can be used to validate form data before
it is submitted to a server. This saves the server from extra processing

• JavaScript can be used to detect the visitor's browser - A JavaScript can be used to detect the
visitor's browser, and - depending on the browser - load another page specifically designed for
that browser

• JavaScript can be used to create cookies - A JavaScript can be used to store and retrieve
information on the visitor's computer

The Real Name is ECMAScript

JavaScript's official name is ECMAScript.

ECMAScript is developed and maintained by the ECMA Organization.

ECMA-262 is the official JavaScript standard.

The language was invented by Brendan Eich at Netscape (with Navigator 2.0), and has appeared in all
Netscape and Microsoft browsers since 1996. The development of ECMA-262 started in 1996, and the
first edition of was adopted by the ECMA General Assembly in June 1997. The standard was approved as
an international ISO (ISO/IEC 16262) standard in 1998.

The development of the standard is still in progress. The HTML <script> tag is used to insert a JavaScript
into an HTML page. Put a JavaScript into an HTML page

The example below shows how to use JavaScript to write text on a web page:

Example

<html>
<body>
<script type="text/javascript"> document.write("Hello World!"); </script>
</body>
</html>

The example below shows how to add HTML tags to the JavaScript:

Example

<html>
<body>
<script type="text/javascript"> document.write("<h1>Hello World!</h1>");</script>
</body>
</html>

Note:

To insert a JavaScript into an HTML page, we use the <script> tag. Inside the <script> tag we use the
type attribute to define the scripting language.

So, the <script type="text/javascript"> and </script> tells where the JavaScript starts and ends:

<html>
<body>
<script type="text/javascript"> ...</script>
</body> </html>

The document.write command is a standard JavaScript command for writing output to a page.

By entering the document.write command between the <script> and </script> tags, the browser
will recognize it as a JavaScript command and execute the code line. In this case the browser will write
Hello World! to the page:

<html>
<body>
<script type="text/javascript"> document.write("Hello World!"); </script>
</body>
</html>

Note: If we had not entered the <script> tag, the browser would have treated the document.write("Hello
World!") command as pure text, and just write the entire line on the page.

How to Handle Simple Browsers

Browsers that do not support JavaScript will display JavaScript as page content.

To prevent them from doing this, and as a part of the JavaScript standard, the HTML comment tag should
be used to "hide" the JavaScript.

Just add an HTML comment tag <! -- Before the first JavaScript statement, and a --> (end of comment)
after the last JavaScript statement, like this:

<html>
<body>
<script type="text/javascript">  </script>
</body>
</html>

The two forward slashes at the end of comment line (//) is the JavaScript comment symbol. This prevents
JavaScript from executing the --> tag

JavaScripts in the body section will be executed WHILE the page loads.

JavaScripts in the head section will be executed when CALLED.

Where to Put the JavaScript

JavaScript’s in a page will be executed immediately while the page loads into the browser. This is not
always what we want. Sometimes we want to execute a script when a page loads, other times when a user
triggers an event.

Scripts in <head>

Scripts to be executed when they are called, or when an event is triggered, go in the head section.

If we place a script in the head section, you will ensure that the script is loaded before anyone uses it.

Example

<html>
<head>
<script type="text/javascript">
function message()
{
alert("This alert box was called with the onload event");
}
</script>
</head>
<body onload="message()"> </body>
</html>

Scripts in <body>

Scripts to be executed when the page loads go in the body section.

If we place a script in the body section, it generates the content of a page.

Example

<html>
<head>
</head>

<body>
document.write("This message is written by JavaScript");
</script>
</body></html>

Scripts in <head> and <body>

We can place an unlimited number of scripts in your document, so we can have scripts in both the body
and the head section.

<html>
<head>
<script type="text/javascript"> .... </script>
</head>
<body><script type="text/javascript">...</script>
</body>

Using an External JavaScript

To run the same JavaScript on several pages, without having to write the same script on every
page, you can write a JavaScript in an external file.

Save the external JavaScript file with a .js file extension.

Note: The external script cannot contain the <script> tag!

To use the external script, point to the .js file in the "src" attribute of the <script> tag:

Example

<html>
<head>
<script type="text/javascript" src="xxx.js"></script>
</head>
<body>
</body>
</html>

Note: Remember to place the script exactly where you normally would write the script!

JavaScript is a sequence of statements to be executed by the browser.

JavaScript is Case Sensitive

Unlike HTML, JavaScript is case sensitive - therefore watch your capitalization closely when you write
JavaScript statements, create or call variables, objects and functions.

JavaScript Statements

A JavaScript statement is a command to a browser. The purpose of the command is to tell the browser
what to do.

This JavaScript statement tells the browser to write "Hello Dolly" to the web page:

document.write("Hello Dolly");

It is normal to add a semicolon at the end of each executable statement. Most people think this is a good
programming practice, and most often you will see this in JavaScript examples on the web.

The semicolon is optional (according to the JavaScript standard), and the browser is supposed to interpret
the end of the line as the end of the statement. Because of this you will often see examples without the
semicolon at the end.

Note: Using semicolons makes it possible to write multiple statements on one line.

JavaScript Code

JavaScript code (or just JavaScript) is a sequence of JavaScript statements. Each statement is executed by
the browser in the sequence they are written. This example will write a heading and two paragraphs to a
web page:

Example

document.write("<h1>This is a heading</h1>");
document.write("<p>This is a paragraph.</p>");
document.write("<p>This is another paragraph.</p>");
</script>

JavaScript Blocks

JavaScript statements can be grouped together in blocks. Blocks start with a left curly bracket

{, and ends with a right curly bracket }.

The purpose of a block is to make the sequence of statements execute together. This example will write a
heading and two paragraphs to a web page:

Example

{
}
</script>

The example above is not very useful. It just demonstrates the use of a block. Normally a block is
used to group statements together in a function or in a condition (where a group of statements should be
executed if a condition is met).

JavaScript comments can be used to make the code more readable.

JavaScript Comments

Comments can be added to explain the JavaScript, or to make the code more readable.

Single line comments start with //.

The following example uses single line comments to explain the code:

Example

<script type="text/javascript"> // Write a heading
document.write("<h1>This is a heading</h1>"); // Write two paragraphs:
</script>

JavaScript Multi-Line Comments

Multi line comments start with /* and end with */. The following example uses a multi line comment to
explain the code:

Example

<script type="text/javascript">/*The code below will write one
heading and two paragraphs */
</script>

Using Comments to Prevent Execution

In the following example the comment is used to prevent the execution of a single code line (can be
suitable for debugging):

Example

//document.write("<h1>This is a heading</h1>");
</script>

In the following example the comment is used to prevent the execution of a code block (can be suitable
for debugging):

Example

<script type="text/javascript">/*document.write("<h1>This is a heading</h1>");

*/</script>

Using Comments at the End of a Line

In the following example the comment is placed at the end of a code line:

Example

document.write("Hello"); // Write "Hello"
document.write(" Dolly!"); // Write " Dolly!" </script>

Variables are "containers" for storing information.

JavaScript Variables

As with algebra, JavaScript variables are used to hold values or expressions.

A variable can have a short name, like x, or a more descriptive name, like carname.

Rules for JavaScript variable names:

• Variable names are case sensitive (y and Y are two different variables)
• Variable names must begin with a letter or the underscore character

Note: Because JavaScript is case-sensitive, variable names are case-sensitive.

Declaring (Creating) JavaScript Variables

Creating variables in JavaScript is most often referred to as "declaring" variables.

You can declare JavaScript variables with the var statement:

var x;
var carname;

After the declaration shown above, the variables are empty (they have no values yet).

However, you can also assign values to the variables when you declare them:

var x=5;
var carname="Volvo";

After the execution of the statements above, the variable x will hold the value 5, and carname will hold
the value Volvo.

Note: When you assign a text value to a variable, use quotes around the value.

Assigning Values to Undeclared JavaScript Variables

If you assign values to variables that have not yet been declared, the variables will automatically be
declared.

These statements:

x=5;
carname="Volvo";

have the same effect as:

var x=5;
var carname="Volvo";

Redeclaring JavaScript Variables

If you redeclare a JavaScript variable, it will not lose its original value.

var x=5;
var x;

After the execution of the statements above, the variable x will still have the value of 5. The value of x is
not reset (or cleared) when you redeclare it.

JavaScript Arithmetic

As with algebra, you can do arithmetic operations with JavaScript variables:

y=x-5;
z=y+5;

You will learn more about the operators that can be used in the next chapter of this tutorial.

= is used to assign values.

+ is used to add values.

The assignment operator = is used to assign values to JavaScript variables.

The arithmetic operator + is used to add values together.

y=5;
z=2;
x=y+z;

The value of x, after the execution of the statements above is 7.

JavaScript Arithmetic Operators

Arithmetic operators are used to perform arithmetic between variables and/or values.

Given that y=5, the table below explains the arithmetic operators:

Operator Description Example Result

+ Addition x=y+2 x=7

- Subtraction x=y-2 x=3

* Multiplication x=y*2 x=10

/ Division x=y/2 x=2.5

% Modulus (division remainder) x=y%2 x=1

++ Increment x=++y x=6

-- Decrement x=--y x=4

JavaScript Assignment Operators

Assignment operators are used to assign values to JavaScript variables.

Given that x=10 and y=5, the table below explains the assignment operators:

Operator Example Same As Result

= x=y x=5

+= x+=y x=x+y x=15

-= x-=y x=x-y x=5

*= x*=y x=x*y x=50

/= x/=y x=x/y x=2

%= x%=y x=x%y x=0

The + Operator Used on Strings

The + operator can also be used to add string variables or text values together. To add two or more string
variables together, use the + operator.

txt1="What a very";
txt2="nice day";
txt3=txt1+txt2;

After the execution of the statements above, the variable txt3 contains "What a verynice day". To add a
space between the two strings, insert a space into one of the strings:

txt1="What a very ";
txt2="nice day";
txt3=txt1+txt2;

or insert a space into the expression:

txt1="What a very";
txt2="nice day";
txt3=txt1+" "+txt2;

After the execution of the statements above, the variable txt3 contains:

"What a very nice day"

Adding Strings and Numbers

The rule is: If you add a number and a string, the result will be a string!

Example

x=5+5;
document.write(x);

x="5"+"5";
document.write(x);

x=5+"5";
document.write(x);

x="5"+5;
document.write(x);

Comparison and Logical operators are used to test for true or false.

Comparison Operators

Comparison operators are used in logical statements to determine equality or difference between variables
or values. Given that x=5, the table below explains the comparison operators:

Operator Description Example

== is equal to x==8 is false

=== is exactly equal to (value and type) x===5 is true
x==="5" is false

!= is not equal x!=8 is true

> is greater than x>8 is false

< is less than x<8 is true

>= is greater than or equal to x>=8 is false

<= is less than or equal to x<=8 is true

How Can it be Used

Comparison operators can be used in conditional statements to compare values and take action depending
on the result:

if (age<18) document.write("Too young");

You will learn more about the use of conditional statements in the next chapter of this tutorial.

Logical Operators

Logical operators are used to determine the logic between variables or values.

Given that x=6 and y=3, the table below explains the logical operators:

Operator Description Example

&& And (x < 10 && y > 1) is true

|| Or (x==5 || y==5) is false

! Not !(x==y) is true

Conditional Operator

JavaScript also contains a conditional operator that assigns a value to a variable based on some condition.

Syntax
variablename=(condition)?value1:value2

Example
greeting=(visitor=="PRES")?"Dear President ":"Dear ";

If the variable visitor has the value of "PRES", then the variable greeting will be assigned the value
"Dear President " else it will be assigned "Dear".

Conditional statements are used to perform different actions based on different conditions.

Conditional Statements

Very often when you write code, you want to perform different actions for different decisions. You can
use conditional statements in your code to do this. In JavaScript we have the following conditional
statements:

• if statement - use this statement to execute some code only if a specified condition is true
• if...else statement - use this statement to execute some code if the condition is true and another
code if the condition is false

• if...else if....else statement - use this statement to select one of many blocks of code to be
executed

• switch statement - use this statement to select one of many blocks of code to be executed

If Statement

Use the if statement to execute some code only if a specified condition is true.

Syntax
if (condition)
{
code to be executed if condition is true
}

Note that if is written in lowercase letters. Using uppercase letters (IF) will generate a JavaScript error!

Example

//Write a "Good morning" greeting if
//the time is less than 10
var d=new Date();

var time=d.getHours();
if (time<10)
{
document.write("<b>Good morning</b>");
} </script>

Notice that there is no ..else.. in this syntax. You tell the browser to execute some code only if the
specified condition is true.

If...else Statement

Use the if....else statement to execute some code if a condition is true and another code if the condition is
not true.

Syntax

if (condition)
{
code to be executed if condition is true
}
else
{
code to be executed if condition is not true
}

Example

//If the time is less than 10, you will get a "Good morning" greeting.
//Otherwise you will get a "Good day" greeting.
var d = new Date();

var time = d.getHours();

if (time < 10)
{
document.write("Good morning!");
}
else
{
document.write("Good day!");
}
</script>

If...else if...else Statement

Use the if....else if...else statement to select one of several blocks of code to be executed.

Syntax
if (condition1)
{
code to be executed if condition1 is true
}
else if (condition2)
{
code to be executed if condition2 is true
}
else
{
code to be executed if condition1 and condition2 are not true
}

Example

var d = new Date();
var time = d.getHours();
if (time<10)
{
document.write("<b>Good morning</b>");
}
else if (time>10 && time<16)
{
document.write("<b>Good day</b>");
}
else
{
document.write("<b>Hello World!</b>");
}
</script>

Conditional statements are used to perform different actions based on different conditions.

The JavaScript Switch Statement

Use the switch statement to select one of many blocks of code to be executed.

Syntax
switch(n)
{
case 1:
execute code block 1
break;
case 2:
execute code block 2
break;
default:
code to be executed if n is different from case 1 and 2
}

This is how it works: First we have a single expression n (most often a variable), that is evaluated once.
The value of the expression is then compared with the values for each case in the structure. If there is a
match, the block of code associated with that case is executed. Use break to prevent the code from
running into the next case automatically.

Example

//You will receive a different greeting based
//on what day it is. Note that Sunday=0,
//Monday=1, Tuesday=2, etc.
var d=new Date();
theDay=d.getDay();
switch (theDay)
{
case 5:
document.write("Finally Friday");
break;
case 6:
document.write("Super Saturday");
break;
case 0:
document.write("Sleepy Sunday");
break;
default:
document.write("I'm looking forward to this weekend!");
}
</script>

JavaScript has three kind of popup boxes: Alert box, Confirm box, and Prompt box.

Alert Box

An alert box is often used if you want to make sure information comes through to the user.

When an alert box pops up, the user will have to click "OK" to proceed.

Syntax
alert("sometext");

Example

<html>

<head>
function showalert()
{
alert("I am an alert box!");
}
</script></head><body>
<input type="button" onclick="showalert()" value="Show alert box" />
</body></html>

Confirm Box

A confirm box is often used if you want the user to verify or accept something.

When a confirm box pops up, the user will have to click either "OK" or "Cancel" to proceed.

If the user clicks "OK", the box returns true. If the user clicks "Cancel", the box returns false.

Syntax
confirm("sometext");

Example

<html><head>
function showconfirm()
{
var r=confirm("Suresh Press a button pls ");
if (r==true)
{
document.write("You pressed OK!");
}
else
{
document.write("You pressed Cancel!");
}
}
<input type="button" onclick="showconfirm()" value="Show confirm box" />

</body></html>

Prompt Box

A prompt box is often used if you want the user to input a value before entering a page.

When a prompt box pops up, the user will have to click either "OK" or "Cancel" to proceed after entering
an input value.

If the user clicks "OK" the box returns the input value. If the user clicks "Cancel" the box returns null.

Syntax
prompt("sometext","defaultvalue");

Example

<html><head>
function show_prompt()
{
var name=prompt("Please enter your name","Harry Potter");
if (name!=null && name!="")
{
document.write("Hello " + name + "! How are you today?");
}
}
<input type="button" onclick="show_prompt()" value="Show prompt box" />
</body></html>

A function will be executed by an event or by a call to the function.

JavaScript Functions

To keep the browser from executing a script when the page loads, you can put your script into a function.

A function contains code that will be executed by an event or by a call to the function.

You may call a function from anywhere within a page (or even from other pages if the function is
embedded in an external .js file).

Functions can be defined both in the <head> and in the <body> section of a document. However, to
assure that a function is read/loaded by the browser before it is called, it could be wise to put functions in
the <head> section.

How to Define a Function

Syntax

function functionname(var1,var2,...,varX)
{ some code }

The parameters var1, var2, etc. are variables or values passed into the function. The { and the } defines
the start and end of the function.

Note: A function with no parameters must include the parentheses () after the function name.

Note: Do not forget about the importance of capitals in JavaScript! The word function must be written in
lowercase letters, otherwise a JavaScript error occurs! Also note that you must call a function with the
exact same capitals as in the function name.

JavaScript Function Example

Example

<html>
<head>
function displaymessage()
{
alert("Hello World!");
}
<form>
<input type="button" value="Click me!" onclick="displaymessage()" />
</form></body></html>

If the line: alert("Hello world!!") in the example above had not been put within a function, it would have
been executed as soon as the line was loaded. Now, the script is not executed before a user hits the input
button. The function displaymessage() will be executed if the input button is clicked.

The return Statement

The return statement is used to specify the value that is returned from the function.

So, functions that are going to return a value must use the return statement.

The example below returns the product of two numbers (a and b):

Example

<html><head>
function product(a,b)
{
return a*b;
}
</script></head>
<body>


document.write(product(4,3));

</script>
</body></html>

The Lifetime of JavaScript Variables

If you declare a variable within a function, the variable can only be accessed within that function. When
you exit the function, the variable is destroyed. These variables are called local variables. You can have
local variables with the same name in different functions, because each is recognized only by the function
in which it is declared.

If we declare a variable outside a function, all the functions on your page can access it. The lifetime of
these variables starts when they are declared, and ends when the page is closed. Loops execute a block of
code a specified number of times, or while a specified condition is true.

JavaScript Loops

Often when you write code, you want the same block of code to run over and over again in a row. Instead
of adding several almost equal lines in a script we can use loops to perform a task like this.

In JavaScript, there are two different kind of loops:

• for - loops through a block of code a specified number of times
• while - loops through a block of code while a specified condition is true

The for Loop

The for loop is used when you know in advance how many times the script should run.

Syntax
for (var=startvalue;var<=endvalue;var=var+increment)
{
code to be executed
}

Example

The example below defines a loop that starts with i=0. The loop will continue to run as long as i is less
than, or equal to 5. i will increase by 1 each time the loop runs.

Note: The increment parameter could also be negative, and the <= could be any comparing statement.

Example

<html><body>
var i=0;
for (i=0;i<=5;i++)
{
document.write("The number is " + i);
document.write("<br />");
}
</script> </body></html>

The while Loop

The while loop loops through a block of code while a specified condition is true.

Syntax
while (var<=endvalue)
{
code to be executed
}

Note: The <= could be any comparing statement.

Example

The example below defines a loop that starts with i=0. The loop will continue to run as long as i is less
than, or equal to 5. i will increase by 1 each time the loop runs:

Example

<html><body>

var i=0;
while (i<=5)
{
i++;
}
</script></body></html>

The do...while Loop

The do...while loop is a variant of the while loop. This loop will execute the block of code ONCE, and
then it will repeat the loop as long as the specified condition is true.

Syntax
do
{
code to be executed
}
while (var<=endvalue);

Example

The example below uses a do...while loop. The do...while loop will always be executed at least once, even
if the condition is false, because the statements are executed before the condition is tested:
Example

<html><body>

var i=0;
do
{
i++;
}

while (i<=5);

The break Statement

The break statement will break the loop and continue executing the code that follows after the loop (if
any).

Example

<html><body>

var i=0;
for (i=0;i<=10;i++)
{
if (i==5)
{
break;
}

document.write("<br />"); }

The continue Statement

The continue statement will break the current loop and continue with the next value.

Example

<html> <body> <script type="text/javascript">
var i=0
for (i=0;i<=10;i++)
{
if (i==3)
{
continue;
}

}
</script></body> </html>

JavaScript For...In Statement

The for...in statement loops through the elements of an array or through the properties of an object.

Syntax
for (variable in object)
{
code to be executed
}

Note: The code in the body of the for...in loop is executed once for each element/property.

Note: The variable argument can be a named variable, an array element, or a property of an object.

Example: Use the for...in statement to loop through an array:
Example

<html>
<body>

var x;

var mycars = new Array();
mycars[0] = "Saab";
mycars[1] = "Volvo";
mycars[2] = "BMW";
for (x in mycars)
{
document.write(mycars[x] + "<br />");
}

Events are actions that can be detected by JavaScript.

Events

By using JavaScript, we have the ability to create dynamic web pages. Events are actions that can be
detected by JavaScript.

Every element on a web page has certain events which can trigger a JavaScript. For example, we can use
the onClick event of a button element to indicate that a function will run when a user clicks on the button.
We define the events in the HTML tags.

Examples of events:

• A mouse click
• A web page or an image loading

• Mousing over a hot spot on the web page

• Selecting an input field in an HTML form

• Submitting an HTML form

• A keystroke

Note: Events are normally used in combination with functions, and the function will not be executed
before the event occurs!

onLoad and onUnload

The onLoad and onUnload events are triggered(cause to happen) when the user enters or leaves the
page.The onLoad event is often used to check the visitor's browser type and browser version, and load the
proper version of the web page based on the information.

Both the onLoad and onUnload events are also often used to deal with cookies that should be set
when a user enters or leaves a page. For example, you could have a popup asking for the user's name
upon his first arrival to your page. The name is then stored in a cookie. Next time the visitor arrives at
your page, you could have another popup saying something like: "Welcome John Doe!".

onFocus, onBlur and onChange

The onFocus, onBlur and onChange events are often used in combination with validation of form fields.

Below is an example of how to use the onChange event. The checkEmail() function will be called
whenever the user changes the content of the field:

<input type="text" size="30" id="email" onchange="checkEmail()">

onSubmit

The onSubmit event is used to validate ALL form fields before submitting it.

Below is an example of how to use the onSubmit event. The checkForm() function will be called
when the user clicks the submit button in the form. If the field values are not accepted, the submit should
be cancelled. The function checkForm() returns either true or false. If it returns true the form will be
submitted, otherwise the submit will be cancelled:

<form method="post" action="xxx.htm" onsubmit="return checkForm()">

onMouseOver and onMouseOut

onMouseOver and onMouseOut are often used to create "animated" buttons. Below is an example of an
onMouseOver event. An alert box appears when an onMouseOver event is detected:

<a href="http://www.Google.com"

onmouseover="alert('An onMouseOver event');return false">

<img src="w3s.gif" alt="Google" /></a>

The try...catch statement allows you to test a block of code for errors.

JavaScript - Catching Errors

When browsing Web pages on the internet, we all have seen a JavaScript alert box telling us there is a
runtime error and asking "Do you wish to debug?". Error message like this may be useful for developers
but not for users. When users see errors, they often leave the Web page.

This chapter will teach you how to catch and handle JavaScript error messages, so you don't lose your
audience.

The try...catch Statement

The try...catch statement allows you to test a block of code for errors. The try block contains the code to
be run, and the catch block contains the code to be executed if an error occurs.

Syntax
try
{
//Run some code here
}
catch(err)
{
//Handle errors here
}

Note that try...catch is written in lowercase letters. Using uppercase letters will generate a JavaScript
error!

Example 1

The example below is supposed to alert "Welcome guest!" when the button is clicked. However, there's a
typo in the message() function. alert() is mis spelled as adddlert(). A JavaScript error occurs. The catch
block catches the error and executes a custom code to handle it. The code displays a custom error
message informing the user what happened:

Example

<html>
<head>
var txt=""
function message()
{
try
{
adddlert("Welcome guest!");
}
catch(err)
{
txt="There was an error on this page.nn";
txt+="Error description: " + err.description + "nn";
txt+="Click OK to continue.nn";
alert(txt);
}
}
</script>
</head>
<body>
<input type="button" onclick="message()" value="View message" />
</body>
</html>

Example 2

The next example uses a confirm box to display a custom message telling users they can click OK to
continue viewing the page or click Cancel to go to the homepage. If the confirm method returns false, the
user clicked Cancel, and the code redirects the user. If the confirm method returns true, the code does
nothing:

Example

<html>
<head>
var txt=""
function message()
{
try
{
adddlert("Welcome guest!");
}
catch(err)
{
txt="There was an error on this page.nn";
txt+="Click OK to continue viewing this page,n";
txt+="or Cancel to return to the home page.nn";
if(!confirm(txt))
{
document.location.href="http://www.w3schools.com/";
}
}
}
</script>
</head>

<body>
<input type="button" value="View message" onclick="message()" />
</body>
</html>

The throw Statement

The throw statement can be used together with the try...catch statement, to create an exception for the
error. Learn about the throw statement in the next chapter.

The throw statement allows you to create an exception.

The Throw Statement

The throw statement allows you to create an exception. If you use this statement together with the
try...catch statement, you can control program flow and generate accurate error messages.

Syntax
throw(exception)

The exception can be a string, integer, Boolean or an object.

Note that throw is written in lowercase letters. Using uppercase letters will generate a JavaScript error!

Example

The example below determines the value of a variable called x. If the value of x is higher than 10, lower
than 0, or not a number, we are going to throw an error. The error is then caught by the catch argument
and the proper error message is displayed:

Example

<html>
<body>
var x=prompt("Enter a number between 0 and 10:","");
try
{
if(x>10)
{
throw "Err1";
}
else if(x<0)
{
throw "Err2";
}
else if(isNaN(x))
{
throw "Err3";
}
}
catch(er)
{
if(er=="Err1")
{
alert("Error! The value is too high");

}
if(er=="Err2")
{
alert("Error! The value is too low");
}
if(er=="Err3")
{
alert("Error! The value is not a number");
}
}
</script>
</body>
</html>

In JavaScript you can add special characters to a text string by using the backslash sign.

Insert Special Characters

The backslash () is used to insert apostrophes, new lines, quotes, and other special characters into a text
string. Look at the following JavaScript code:

var txt="We are the so-called "Vikings" from the north.";
document.write(txt);

In JavaScript, a string is started and stopped with either single or double quotes. This means that the
string above will be chopped to: We are the so-called

To solve this problem, you must place a backslash () before each double quote in "Viking". This turns
each double quote into a string literal:

var txt="We are the so-called "Vikings" from the north.";
document.write(txt);

JavaScript will now output the proper text string: We are the so-called "Vikings" from the north.

Here is another example:

document.write ("You & I are singing!");

The example above will produce the following output:

You & I are singing!

The table below lists other special characters that can be added to a text string with the backslash sign:

Code Outputs

' single quote

" double quote

& ampersand

backslash

n new line

r carriage return

t tab

b backspace

f form feed

Some other important things to know when scripting with JavaScript.

JavaScript is Case Sensitive

A function named "myfunction" is not the same as "myFunction" and a variable named "myVar" is not
the same as "myvar".

JavaScript is case sensitive - therefore watch your capitalization closely when you create or call variables,
objects and functions.

White Space

JavaScript ignores extra spaces. You can add white space to your script to make it more readable. The
following lines are equivalent:

name="Hege";
name = "Hege";

Break up a Code Line

You can break up a code line within a text string with a backslash. The example below will be displayed
properly:

document.write("Hello
World!");

However, you cannot break up a code line like this:

document.write
("Hello World!");

Object Oriented Programming

JavaScript is an Object Oriented Programming (OOP) language. An OOP language allows you to define
your own objects and make your own variable types.

However, creating your own objects will be explained later, in the Advanced JavaScript section. We will
start by looking at the built-in JavaScript objects, and how they are used. The next pages will explain each
built-in JavaScript object in detail.

Note that an object is just a special kind of data. An object has properties and methods.

Properties

Properties are the values associated with an object. In the following example we are using the length
property of the String object to return the number of characters in a string:

var txt="Hello World!";
document.write(txt.length);
</script>

The output of the code above will be:

12

Methods

Methods are the actions that can be performed on objects.

In the following example we are using the toUpperCase() method of the String object to display a text in
uppercase letters:

var str="Hello world!";
document.write(str.toUpperCase());
</script>

The output of the code above will be:

HELLO WORLD!

The String object is used to manipulate a stored piece of text.

Complete String Object Reference

The reference contains a brief description and examples of use for each property and method!

String object

The String object is used to manipulate a stored piece of text.

Examples of use:

The following example uses the length property of the String object to find the length of a string:

var txt="Hello world!";
document.write(txt.length);

The code above will result in the following output:

12

The following example uses the toUpperCase() method of the String object to convert a string to
uppercase letters:

var txt="Hello world!";
document.write(txt.toUpperCase());


HELLO WORLD!

Create a Date Object

The Date object is used to work with dates and times.

The following code create a Date object called myDate:

var myDate=new Date()

Note: The Date object will automatically hold the current date and time as its initial value!

Set Dates

We can easily manipulate the date by using the methods available for the Date object.

In the example below we set a Date object to a specific date (14th January 2010):

var myDate=new Date();
myDate.setFullYear(2010,0,14);

And in the following example we set a Date object to be 5 days into the future:

myDate.setDate(myDate.getDate()+5);

Note: If adding five days to a date shifts the month or year, the changes are handled automatically by the
Date object itself!

Compare Two Dates

The Date object is also used to compare two dates.

The following example compares today's date with the 14th January 2010:

myDate.setFullYear(2010,0,14);
var today = new Date();

if (myDate>today)
{
alert("Today is before 14th January 2010");
}
else

{
alert("Today is after 14th January 2010");
}

The Array object is used to store multiple values in a single variable.

What is an Array?

An array is a special variable, which can hold more than one value, at a time.

If you have a list of items (a list of car names, for example), storing the cars in single variables could look
like this:

cars1="Saab";
cars2="Volvo";
cars3="BMW";

However, what if you want to loop through the cars and find a specific one? And what if you had not 3
cars, but 300?

The best solution here is to use an array!

An array can hold all your variable values under a single name. And you can access the values by
referring to the array name.

Each element in the array has its own ID so that it can be easily accessed.

Create an Array

The following code creates an Array object called myCars:

var myCars=new Array();

There are two ways of adding values to an array (you can add as many values as you need to define as
many variables you require).

1:

var myCars=new Array();
myCars[0]="Saab";
myCars[1]="Volvo";

myCars[2]="BMW";

You could also pass an integer argument to control the array's size:

var myCars=new Array(3);
myCars[0]="Saab";
myCars[1]="Volvo";
myCars[2]="BMW";

2:

var myCars=new Array("Saab","Volvo","BMW");

Note: If you specify numbers or true/false values inside the array then the type of variables will be
numeric or Boolean instead of string.

Access an Array

You can refer to a particular element in an array by referring to the name of the array and the index
number. The index number starts at 0.

The following code line:

document.write(myCars[0]);

will result in the following output:

Saab

Modify Values in an Array

To modify a value in an existing array, just add a new value to the array with a specified index number:

myCars[0]="Opel";

Now, the following code line:

document.write(myCars[0]);

will result in the following output:

Opel

The Array object is used to store multiple values in a single variable.

The reference contains a brief description and examples of use for each property and method!

Create a Boolean Object

The Boolean object represents two values: "true" or "false". The following code creates a Boolean object
called myBoolean:

var myBoolean=new Boolean();

Note: If the Boolean object has no initial value or if it is 0, -0, null, "", false, undefined, or NaN, the
object is set to false. Otherwise it is true (even with the string "false")!

All the following lines of code create Boolean objects with an initial value of false:

var myBoolean=new Boolean();
var myBoolean=new Boolean(0);
var myBoolean=new Boolean(null);
var myBoolean=new Boolean("");
var myBoolean=new Boolean(false);
var myBoolean=new Boolean(NaN);

And all the following lines of code create Boolean objects with an initial value of true:

var myBoolean=new Boolean(true);
var myBoolean=new Boolean("true");
var myBoolean=new Boolean("false");
var myBoolean=new Boolean("Richard");

Math Object

The Math object allows you to perform mathematical tasks.

The Math object includes several mathematical constants and methods.

Syntax for using properties/methods of Math:

var pi_value=Math.PI;
var sqrt_value=Math.sqrt(16);

Note: Math is not a constructor. All properties and methods of Math can be called by using Math as an
object without creating it.

Mathematical Constants

JavaScript provides eight mathematical constants that can be accessed from the Math object. These are: E,
PI, square root of 2, square root of 1/2, natural log of 2, natural log of 10, base-2 log of E, and base-10 log
of E.

You may reference these constants from your JavaScript like this:

Math.E
Math.PI
Math.SQRT2
Math.SQRT1_2
Math.LN2
Math.LN10
Math.LOG2E
Math.LOG10E

Mathematical Methods

In addition to the mathematical constants that can be accessed from the Math object there are also several
methods available.

The following example uses the round() method of the Math object to round a number to the nearest
integer:

document.write(Math.round(4.7));


5

The following example uses the random() method of the Math object to return a random number between
0 and 1:

document.write(Math.random());

The code above can result in the following output:

0.9039979251610644

The following example uses the floor() and random() methods of the Math object to return a random
number between 0 and 10:

document.write(Math.floor(Math.random()*11));

The code above can result in the following output:

10

What is RegExp

RegExp, is short for regular expression.

When you search in a text, you can use a pattern to describe what you are searching for. RegExp IS this
pattern.

A simple pattern can be a single character.

A more complicated pattern consists of more characters, and can be used for parsing, format checking,
substitution and more.

You can specify where in the string to search, what type of characters to search for, and more.

Defining RegExp

The RegExp object is used to store the search pattern.

We define a RegExp object with the new keyword. The following code line defines a RegExp object
called patt1 with the patter n "e":

var patt1=new RegExp("e");

When you use this RegExp object to search in a string, you will find the letter "e".

Methods of the RegExp Object

The RegExp Object has 3 methods: test(), exec(), and compile().

test()

The test() method searches a string for a specified value. Returns true or false

Example

document.write(patt1.test("The best things in life are free"));

Since there is an "e" in the string, the output of the code above will be:

true

exec()

The exec() method searches a string for a specified value. Returns the text of the found value. If no match
is found, it returns null

Example 1


document.write(patt1.exec("The best things in life are free"));

Since there is an "e" in the string, the output of the code above will be:

e

We can add a second parameter to the RegExp object, to specify your search. For example; if you want to
find all occurrences of a character, you can use the "g" parameter ("global").

When using the "g" parameter, the exec() method works like this:

• Finds the first occurence of "e", and stores its position
• If you run exec() again, it starts at the stored position, and finds the next occurence of "e", and
stores its position

Example 2

var patt1=new RegExp("e","g");
do
{
result=patt1.exec("The best things in life are free");
document.write(result);
}
while (result!=null)

Since there is six "e" letters in the string, the output of the code above will be:

eeeeeenull

compile()

The compile() method is used to change the RegExp. compile() can change both the search pattern, and
add or remove the second parameter.

Example

patt1.compile("d");

Since there is an "e" in the string, but not a "d", the output of the code above will be:

truefalse

In addition to the built-in JavaScript objects, you can also access and manipulate all of the HTML DOM
objects with JavaScript.

More JavaScript Objects

Follow the links to learn more about the objects and their collections, properties, methods and events.

Object Description

Window The top level object in the JavaScript hierarchy. The Window object represents a
browser window. A Window object is created automatically with every instance
of a <body> or <frameset> tag

Navigator Contains information about the client's browser

Screen Contains information about the client's display screen

History Contains the visited URLs in the browser window

Location Contains information about the current URL

The HTML DOM

The HTML DOM is a W3C standard and it is an abbreviation for the Document Object Model for HTML.

The HTML DOM defines a standard set of objects for HTML, and a standard way to access and manipulate
HTML documents. All HTML elements, along with their containing text and attributes, can be accessed
through the DOM. The contents can be modified or deleted, and new elements can be created.

The HTML DOM is platform and language independent. It can be used by any programming language like
Java, JavaScript, and VBScript. Follow the links below to learn more about how to access and manipulate
each DOM object with JavaScript:

Object Description

Document Represents the entire HTML document and can be used to access all elements in
a page

Anchor Represents an <a> element

Area Represents an <area> element inside an image-map

Base Represents a <base> element

Body Represents the <body> element

Button Represents a <button> element

Event Represents the state of an event

Form Represents a <form> element

Frame Represents a <frame> element

Frameset Represents a <frameset> element

Iframe Represents an <iframe> element

Image Represents an <img> element

Input button Represents a button in an HTML form

Input checkbox Represents a checkbox in an HTML form

Input file Represents a fileupload in an HTML form

Input hidden Represents a hidden field in an HTML form

Input password Represents a password field in an HTML form

Input radio Represents a radio button in an HTML form

Input reset Represents a reset button in an HTML form

Input submit Represents a submit button in an HTML form

Input text Represents a text-input field in an HTML form

Link Represents a <link> element

Meta Represents a <meta> element

Option Represents an <option> element

Select Represents a selection list in an HTML form

Style Represents an individual style statement

Table Represents a <table> element

TableData Represents a <td> element

TableRow Represents a <tr> element

Textarea Represents a <textarea> element

The JavaScript Navigator object contains information about the visitor's browser.

Browser Detection

Almost everything in this tutorial works on all JavaScript-enabled browsers. However, there are some
things that just don't work on certain browsers - especially on older browsers.

So, sometimes it can be very useful to detect the visitor's browser, and then serve up the appropriate
information.

The best way to do this is to make your web pages smart enough to look one way to some browsers and
another way to other browsers.

JavaScript includes an object called the Navigator object, that can be used for this purpose.

The Navigator object contains information about the visitor's browser name, version, and more.

The Navigator Object

The JavaScript Navigator object contains all information about the visitor's browser. We are going to look
at two properties of the Navigator object:

• appName - holds the name of the browser
• appVersion - holds, among other things, the version of the browser

Example

<html>
<body>

var browser=navigator.appName;

var b_version=navigator.appVersion;
var version=parseFloat(b_version);
document.write("Browser name: "+ browser);

document.write("Browser version: "+ version);
</script>
</body>
</html>

The variable browser in the example above holds the name of the browser, i.e. "Netscape" or "Microsoft
Internet Explorer".

The appVersion property in the example above returns a string that contains much more information than
just the version number, but for now we are only interested in the version number. To pull the version
number out of the string we are using a function called parseFloat(), which pulls the first thing that looks
like a decimal number out of a string and returns it.

IMPORTANT! The version number is WRONG in IE 5.0 or later! Microsoft starts the appVersion string
with the number 4.0. in IE 5.0 and IE 6.0!!! Why did they do that??? However, JavaScript is the same in
IE6, IE5 and IE4, so for most scripts it is ok.

The example below displays a different alert, depending on the visitor's browser:

Example

<html><head>
function detectBrowser()
{
var browser=navigator.appName; var b_version=navigator.appVersion;
if ((browser=="Netscape"||browser=="Microsoft Internet Explorer")
&& (version>=4))
{
alert("Your browser is good enough!");
}
else
{
alert("It's time to upgrade your browser!");
}

}
</script></head>
<body onload="detectBrowser()"></body></html>

JavaScript Cookies

A cookie is often used to identify a user.

What is a Cookie?

A cookie is a variable that is stored on the visitor's computer. Each time the same computer requests a
page with a browser, it will send the cookie too. With JavaScript, you can both create and retrieve cookie
values.

Examples of cookies:

• Name cookie - The first time a visitor arrives to your web page, he or she must fill in her/his
name. The name is then stored in a cookie. Next time the visitor arrives at your page, he or she
could get a welcome message like "Welcome John Doe!" The name is retrieved from the stored
cookie
• Password cookie - The first time a visitor arrives to your web page, he or she must fill in a
password. The password is then stored in a cookie. Next time the visitor arrives at your page, the
password is retrieved from the cookie

• Date cookie - The first time a visitor arrives to your web page, the current date is stored in a
cookie. Next time the visitor arrives at your page, he or she could get a message like "Your last
visit was on Tuesday August 11, 2005!" The date is retrieved from the stored cookie

Create and Store a Cookie

In this example we will create a cookie that stores the name of a visitor. The first time a visitor arrives to
the web page, he or she will be asked to fill in her/his name. The name is then stored in a cookie. The
next time the visitor arrives at the same page, he or she will get welcome message.

First, we create a function that stores the name of the visitor in a cookie variable:

function setCookie(c_name,value,expiredays)
{
var exdate=new Date();
exdate.setDate(exdate.getDate()+expiredays);
document.cookie=c_name+ "=" +escape(value)+
((expiredays==null) ? "" : ";expires="+exdate.toGMTString());
}

The parameters of the function above hold the name of the cookie, the value of the cookie, and
the number of days until the cookie expires. In the function above we first convert the number of days to a
valid date, then we add the number of days until the cookie should expire. After that we store the cookie
name, cookie value and the expiration date in the document.cookie object.

Then, we create another function that checks if the cookie has been set:

function getCookie(c_name)
{
if (document.cookie.length>0)
{
c_start=document.cookie.indexOf(c_name + "=");
if (c_start!=-1)
{
c_start=c_start + c_name.length+1;
c_end=document.cookie.indexOf(";",c_start);
if (c_end==-1) c_end=document.cookie.length;
return unescape(document.cookie.substring(c_start,c_end));
}
}
return "";
}

The function above first checks if a cookie is stored at all in the document.cookie object. If the
document.cookie object holds some cookies, then check to see if our specific cookie is stored. If our
cookie is found, then return the value, if not - return an empty string.

Last, we create the function that displays a welcome message if the cookie is set, and if the cookie is not
set it will display a prompt box, asking for the name of the user:

function checkCookie()
{
username=getCookie('username');
if (username!=null && username!="")
{
alert('Welcome again '+username+'!');
}
else
{
username=prompt('Please enter your name:',"");
{
setCookie('username',username,365);
}
}

}

All together now:

Example

<html>
<head>
{
{
if (c_start!=-1)
{
c_start=c_start + c_name.length+1;
if (c_end==-1) c_end=document.cookie.length;
}
}
return "";
}
{
document.cookie=c_name+ "=" +escape(value)+
((expiredays==null) ? "" : ";expires="+exdate.toGMTString());
}
{
{
}
else
{

{
}
}
}
</script>
</head>
<body onload="checkCookie()">
</body>
</html>

The example above runs the checkCookie() function when the page loads.

JavaScript Form Validation

JavaScript can be used to validate data in HTML forms before sending off the content to a server.

Form data that typically are checked by a JavaScript could be:

• has the user left required fields empty?
• has the user entered a valid e-mail address?

• has the user entered a valid date?

• has the user entered text in a numeric field?

Required Fields

The function below checks if a required field has been left empty. If the required field is blank, an alert
box alerts a message and the function returns false. If a value is entered, the function returns true (means
that data is OK):

function validate_required(field,alerttxt)
{
with (field)
{
if (value==null||value=="")
{
alert(alerttxt);

return false;
}
else
{
return true;

}
}
}

The entire script, with the HTML form could look something like this:

<html>
<head>
function validate_ required(field,alerttxt)
{
with (field)
{
if (value==null||value=="")
{
alert(alerttxt);return false;
}
else
{
return true;
}
}
}
function validate_form(thisform)
{
with (thisform)
{
if (validate_ required(email,"Email must be filled out!")==false)
{

email.focus();

return false;

}
}
}
</script>
</head>
<body>
<form action="submit.htm" onsubmit="return validate_form(this)" method="post">
Email: <input type="text" name="email" size="30">
<input type="submit" value="Submit">
</form>

</body>
</html>

E-mail Validation

The function below checks if the content has the general syntax of an email.

This means that the input data must contain at least an @ sign and a dot (.). Also, the @ must not be the
first character of the email address, and the last dot must at least be one character after the @ sign:

function validate_email(field,alerttxt)
{
with (field)
{
apos=value.indexOf("@");
dotpos=value.lastIndexOf(".");
if (apos<1||dotpos-apos<2)
{alert(alerttxt);return false;}
else {return true;}
}
}

The entire script, with the HTML form could look something like this:

<html>
<head>
function validate_email(field,alerttxt)
{
with (field)
{
apos=value.indexOf("@");
dotpos=value.lastIndexOf(".");
if (apos<1||dotpos-apos<2)
{alert(alerttxt);return false;}
else {return true;}
}
}
function validate_form(thisform)
{
with (thisform)
{
if (validate_email(email,"Not a valid e-mail address!")==false)

{email.focus();return false;}
}
}
</script>
</head>
<body>
<form action="submit.htm" onsubmit="return validate_form(this);" method="post">
Email: <input type="text" name="email" size="30">
<input type="submit" value="Submit">
</form>
</body>
</html>

JavaScript Animation

With JavaScript we can create animated images.

JavaScript Animation

It is possible to use JavaScript to create animated images. The trick is to let a JavaScript change between
different images on different events.

In the following example we will add an image that should act as a link button on a web page. We
will then add an onMouseOver event and an onMouseOut event that will run two JavaScript functions
that will change between the images.

The HTML Code

The HTML code looks like this:

<a href="http://www.w3schools.com" target="_blank">
<img border="0" alt="Visit W3Schools!" src="b_pink.gif" id="b1"
onmouseOver="mouseOver()" onmouseOut="mouseOut()" /></a>

Note that we have given the image an id, to make it possible for a JavaScript to address it later.

The onMouseOver event tells the browser that once a mouse is rolled over the image, the browser should
execute a function that will replace the image with another image.

The onMouseOut event tells the browser that once a mouse is rolled away from the image, another
JavaScript function should be executed. This function will insert the original image again.

The JavaScript Code

The changing between the images is done with the following JavaScript:

function mouseOver()
{
document.getElementById("b1").src ="b_blue.gif";
}
function mouseOut()
{
document.getElementById("b1").src ="b_pink.gif";
}
</script>

The function mouseOver() causes the image to shift to "b_blue.gif".

The function mouseOut() causes the image to shift to "b_pink.gif".

The Entire Code

Example

<html><head>
{
}
function mouseOut()
{
}
</script>
</head><body>
<img border="0" alt="Visit W3Schools!" src="b_pink.gif" id="b1"
onmouseover="mouseOver()" onmouseout="mouseOut()" /></a>
</body></html>

JavaScript Image Maps

An image-map is an image with clickable regions.

HTML Image Maps

From our HTML tutorial we have learned that an image-map is an image with clickable regions.
Normally, each region has an associated hyperlink. Clicking on one of the regions takes you to the
associated link.

Adding some JavaScript

We can add events (that can call a JavaScript) to the <area> tags inside the image map. The <area> tag
supports the onClick, onDblClick, onMouseDown, onMouseUp, onMouseOver, onMouseMove,
onMouseOut, onKeyPress, onKeyDown, onKeyUp, onFocus, and onBlur events.

Here's the HTML image-map example, with some JavaScript added:

Example

<html><head>
function writeText(txt)
{
document.getElementById("desc").innerHTML=txt;
}
</script>
</head>
<body>
<img src="planets.gif" width="145" height="126"
alt="Planets" usemap="#planetmap" />
<map name="planetmap">

<area shape ="rect" coords ="0,0,82,126"
onMouseOver="writeText('The Sun and the gas giant planets like Jupiter
are by far the largest objects in our Solar System.')"
href ="sun.htm" target ="_blank" alt="Sun" />

<area shape ="circle" coords ="90,58,3"
onMouseOver="writeText('The planet Mercury is very difficult to study
from the Earth because it is always so close to the Sun.')"
href ="mercur.htm" target ="_blank" alt="Mercury" />

<area shape ="circle" coords ="124,58,8"
onMouseOver="writeText('Until the 1960s, Venus was often considered a
twin sister to the Earth because Venus is the nearest planet to us, and
because the two planets seem to share many characteristics.')"
href ="venus.htm" target ="_blank" alt="Venus" />
</map>
<p id="desc"></p>
</body>
</html>

JavaScript Timing Events

JavaScript can be executed in time-intervals.
1

2 This is called timing events.

3

4

5

6

7

8

9

10

11

12

JavaScript Timing Events

With JavaScript, it is possible to execute some code after a specified time-interval. This is called timing
events.

It's very easy to time events in JavaScript. The two key methods that are used are:

• setTimeout() - executes a code some time in the future
• clearTimeout() - cancels the setTimeout()

Note: The setTimeout() and clearTimeout() are both methods of the HTML DOM Window object.

The setTimeout() Method

Syntax
var t=setTimeout("javascript statement",milliseconds);

The setTimeout() method returns a value - In the statement above, the value is stored in a variable called
t. If you want to cancel this setTimeout(), you can refer to it using the variable name.

The first parameter of setTimeout() is a string that contains a JavaScript statement. This statement could
be a statement like "alert('5 seconds!')" or a call to a function, like "alertMsg()".

The second parameter indicates how many milliseconds from now you want to execute the first
parameter.

Note: There are 1000 milliseconds in one second.

Example

When the button is clicked in the example below, an alert box will be displayed after 5 seconds.

Example

<html>
<head>
function timedMsg()
{
var t=setTimeout("alert('5 seconds!')",5000);
}

</script>
</head><body><form>
<input type="button" value="Display timed alertbox!"
onClick="timedMsg()" /></form></body></html>

Example - Infinite Loop

To get a timer to work in an infinite loop, we must write a function that calls itself. In the example below,
when the button is clicked, the input field will start to count (for ever), starting at 0:

Example

<html>
<head>
var c=0
var t
function timedCount()
{
document.getElementById('txt').value=c;
c=c+1;
t=setTimeout("timedCount()",1000);
}
</script></head>
<body><form>
<input type="button" value="Start count!" onClick="timedCount()" />
<input type="text" id="txt" />

The clearTimeout() Method

Syntax
clearTimeout(setTimeout_variable)

Example

The example below is the same as the "Infinite Loop" example above. The only difference is that we have
now added a "Stop Count!" button that stops the timer:

Example

<html><head>
var c=0
var t
{
c=c+1;
}
function stopCount()
{
clearTimeout(t);
}
</script>
</head><body><form>
<input type="button" value="Start count!" onClick="timedCount()" />
<input type="text" id="txt" />
<input type="button" value="Stop count!" onClick="stopCount()" />

Another Example

<html><head><script type="text/javascript">

function timedText()

{

var t1=setTimeout("document.getElementById('txt').value='2 seconds!'",2000);



}


<form>

<input type="button" value="Display timed text!" onClick="timedText()">

<input type="text" id="txt">

</form>

<p>Click on the button above. The input field will tell you when two, four, and six seconds have
passed.</p>

</body></html>

Out Put

6 seconds!

Click on the button above. The input field will tell you when two, four, and six seconds have passed.

Another Example

<html>

<head>


function startTime()

{

var today=new Date(); var h=today.getHours(); var m=today.getMinutes(); var s=today.getSeconds();

// add a zero in front of numbers<10

m=checkTime(m); s=checkTime(s); document.getElementById('txt').innerHTML=h+":"+m+":"+s;

t=setTimeout('startTime()',500);

}

function checkTime(i)

{

if (i<10)

{ i="0" + i; }

return i;

}

</script></head>

<body onload="startTime()">

<div id="txt"></div>

</body></html
>

JavaScript Objects

Earlier in this tutorial we have seen that JavaScript has several built-in objects, like String, Date, Array,
and more. In addition to these built-in objects, you can also create your own.

An object is just a special kind of data, with a collection of properties and methods.

Let's illustrate with an example: A person is an object. Properties are the values associated with the
object. The persons' properties include name, height, weight, age, skin tone, eye color, etc. All persons
have these properties, but the values of those properties will differ from person to person. Objects also
have methods. Methods are the actions that can be performed on objects. The persons' methods could be
eat(), sleep(), work(), play(), etc.

Properties

The syntax for accessing a property of an object is:

objName.propName

You can add properties to an object by simply giving it a value. Assume that the personObj already exists
- you can give it properties named firstname, lastname, age, and eyecolor as follows:

personObj.firstname="John";
personObj.lastname="Doe";
personObj.age=30;
personObj.eyecolor="blue";

document.write(personObj.firstname);

The code above will generate the following output:

John

Methods

An object can also contain methods.

We can call a method with the following syntax:

objName.methodName()

Note: Parameters required for the method can be passed between the parentheses.

To call a method called sleep() for the personObj:

personObj.sleep();

Creating Your Own Objects

There are different ways to create a new object:

1. Create a direct instance of an object

The following code creates an instance of an object and adds four properties to it:

personObj=new Object();
personObj.firstname="John";
personObj.lastname="Doe";
personObj.age=50;
personObj.eyecolor="blue";

Adding a method to the personObj is also simple. The following code adds a method called eat() to the
personObj:

personObj.eat=eat;

2. Create a template of an object

The template defines the structure of an object:

function person(firstname,lastname,age,eyecolor)
{
this.firstname=firstname;
this.lastname=lastname;
this.age=age;
this.eyecolor=eyecolor;
}

Notice that the template is just a function. Inside the function you need to assign things to
this.propertyName. The reason for all the "this" stuff is that you're going to have more than one person at

a time (which person you're dealing with must be clear). That's what "this" is: the instance of the object at
hand.

Once you have the template, you can create new instances of the object, like this:

myFather=new person("John","Doe",50,"blue"); myMother=new person("Sally","Rally",48,"green");

You can also add some methods to the person object. This is also done inside the template:

function person(firstname,lastname,age,eyecolor)
{
this.firstname=firstname;
this.lastname=lastname;
this.age=age;
this.eyecolor=eyecolor;

this.newlastname=newlastname; }

Note that methods are just functions attached to objects. Then we will have to write the newlastname()
function:

function newlastname(new_lastname)
{
this.lastname=new_lastname;
}

The newlastname() function defines the person's new last name and assigns that to the person. JavaScript
knows which person you're talking about by using "this.". So, now you can write:
myMother.newlastname("Doe").

Advanced Java script Examples
1. Detect the Visitors Browser Version

<html>
<body>
document.write("Browser name: "+ browser);
document.write("Browser version: "+ version);
</script>
</body>
</html>

Output

Browser name: Microsoft Internet Explorer
Browser version: 4

2. All Details about Visitors Browser

<html>
<body>
var x = navigator;
document.write("CodeName=" + x.appCodeName);
document.write("MinorVersion=" + x.appMinorVersion);
document.write("Name=" + x.appName);
document.write("Version=" + x.appVersion);
document.write("CookieEnabled=" + x.cookieEnabled);
document.write("CPUClass=" + x.cpuClass);
document.write("OnLine=" + x.onLine);
document.write("Platform=" + x.platform);
document.write("UA=" + x.userAgent);
document.write("BrowserLanguage=" + x.browserLanguage);
document.write("SystemLanguage=" + x.systemLanguage);

4. Create a Welcome Cookie

<html>
<head>
{
{
if (c_start!=-1)
{
c_start=c_start + c_name.length+1 ;
if (c_end==-1) c_end=document.cookie.length
}
}
return ""
}

{
document.cookie=c_name+ "=" +escape(value)+((expiredays==null) ? "" : ";
expires="+exdate.toGMTString());
}

{
{
}
else
{
{
}
}
}
</script>
</head>
<body onLoad="checkCookie()">
</body>
</html>

5. Animation Image Button

<html>
<head>
{
}
function mouseOut()
{
}
</script>
</head>
<body>
<img border="0" alt="Visit W3Schools!" src="b_pink.gif" id="b1" width="26" height="26"
onmouseover="mouseOver()" onmouseout="mouseOut()" /></a>
</body>
</html>

6. Simple Timing

<html>
<head>
function timedMsg()
{
var t=setTimeout("alert('5 seconds!')",5000);
}
</script>
</head>
<body>
<form>
<input type="button" value="Display timed alertbox!" onClick = "timedMsg()">
</form>
<p>Click on the button above. An alert box will be displayed after 5 seconds.</p>
</body>
</html>

7. Another Simple Timing

<html>
<head>
function timedText()
{

}
</script>
</head>
<body>
<form>
<input type="button" value="Display timed text!" onClick="timedText()">
</form>
<p>Click on the button above. The input field will tell you when two, four, and six seconds have
passed.</p>
</body>
</html>

8. Timing Event with Infinite Loop

<html>
<head>
var c=0;
var t;
{
c=c+1;
}
</script>
</head>
<body>
<form>
<input type="button" value="Start count!" onClick="timedCount()">
</form>
<p>Click on the button above. The input field will count for ever, starting at 0.</p>
</body>
</html>

9. Timing Event with Infinite Loop with a Button

<html>
<head>
var c=0;
var t;
{
c=c+1;
}

Basics java scripts

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