Lecture 5 javascript

Lecture -5
Javascript
Mujtaba Haider

Objectives
• Introduction to JavaScript
– Introduction to JavaScript programming language
– Using Script tag
– Inserting Java Script into tags
– Linking Java Script from separate files
• JavaScript expression and Operators
– Defining and naming variables
– Data Types
– Expression
– Operators – Arithmetic, String, Logical, Assignment,
typeof

Objectives (Contd.)
• Functions and Flow Control
– Flow Control
• If…else
• For loops
• while loops
• Break and continue statements
– Using JavaScript functions
• Built in functions
• User defined functions
• Returning values from functions
• Events, Event Handlers

Objectives (Contd.)
• Objects and Arrays
– Properties and Methods
– Browser Object Hierarchy
– Addressing Objects
– Creating Objects
– Objects and Variables
– External Objects
– Security Implications
– Arrays and Objects

Objectives (Contd.)
• Document Object Model
– Introduction to DOM
– The Navigator Object
– The Window Object
– Communicating between windows
– Working With Frames in the DOM
– The Document object
– The Location & History Object
– Image Object
– Link Object

Objectives (Contd.)
• Form Validation The Form Object Model
– Recap of Form Elements
– Form Tag Events
– Controlling Submission
– Forms as Navigation
– List Events
– Buttons
– Text Processing

Objectives (Contd.)
• Cookies
– Introduction to HTTP Cookies
– Formatting Cookies
– Persisting Cookies
– Cookie Security
– JavaScript & Cookies
– Reading / Writing Cookies
– Modifying and deleting Cookies

Introduction to Java Scripts
• What is JavaScript???
– JavaScript is a scripting Language created by
Netscape
What is a
Scripting
Language???
•Scripting Language is a lightweight
programming language.
• Scripting Languages are not
needed to be compiled.
•The language is interpreted at
runtime.

Introduction to JavaScript
(Contd.)
– A JavaScript is usually directly embedded in an
HTML page.
– External JavaScripts can be created which can be
used by HTML pages.
– JavaScript adds interactivity to HTML pages.
– JavaScript's are integrated into the browsing
environment.

Introduction to JavaScript
(Contd.)
Is
JavaScript
same as
Java???
• Java is a programming
language which requires
compilation and interpretation.
• Java is used to make large
scale applications.
• JavaScript is a scripting
language which just requires
interpretation. The script is
some set of commands which
the browser interprets.
• JavaScript is used to add
interactivity in HTML Pages.

Types of JavaScript
• Client-Side JavaScript (CSJS) -- an extended
version of JavaScript that enables the enhancement
and manipulation of web pages and client browsers.
• Server-Side JavaScript (SSJS) -- an extended
version of JavaScript that enables back-end access to
databases, file systems, and servers.
• Core JavaScript -- the base JavaScript language.

Core JavaScript
• Core JavaScript encompasses all of the statements,
operators, objects, and functions that make up the
basic JavaScript language.
• The following objects are part of core JavaScript:
– array
– date
– math
– number
– string

Client Side Java Scripting
• CSJS is composed of core JavaScript and many
additional objects, such as the following:
– document
– form
– frame
– window
– Navigator
– History

Server Side JavaScript
• SSJS is composed of core JavaScript and additional
objects and functions for accessing databases and file
systems, sending e-mail, and so on.

Uses of JavaScript (Client Side)
• Menus for Navigation
• Form Validation
• Popup Windows
• Password Protecting
• Math Functions
• Special effects with document and background
• Status bar manipulation
• Messages
• Mouse Cursor Effects
• Links

Syntax rules of JavaScript
• Statements may or may not contain a semicolon at the
end.
• Multiple statements on one line must be separated by a
semicolon.
• JavaScript is case sensitive.

Using <script> tag
• The HTML <script> tag is used to enter JavaScript into
a HTML.
• The <script> tag can be embedded within
– <head> tag.
– <body> tag.
• JavaScript in the head section will be executed when
called.
• JavaScript in the body section will be executed while
the HTML page is loaded.
• Unlimited number of JavaScript’s can be placed both in
head and body section in a HTML document.

Using <script> tag
Eg:
<html>
<head><title>Example</title>
</head>
<body>
<script type="text/javascript">
document.write("Hello World!")
</script>
</body>
</html>
Is a standard command for writing
output to a page

How to Handle Older Browsers
• Browsers that do not support JavaScript will display the
script as it is. Use the HTML comment tag to prevent
this.
Eg.

</script>
The two forward slashes at the end of comment line
(//) are a JavaScript comment symbol. This
prevents the JavaScript compiler from compiling
the line.

Using an External JavaScript
• A JavaScript can be written in an external file, which
can be used by different HTML pages.
• The external script cannot contain the <script> tag.
• The external file needs to end with the .js extension.

Using External JavaScript
(contd.)
document.write("This line
has been writen in the
External JavaScript!!!")
External.js
<html>
<head><title>Example</title>
</head>
<body>
<script src="External.js">
</script>>
<p >
This line has been written in the
html page!!!
</p>
</body>
</html>
JavaScript.html

JavaScript Variables and
expression
• JavaScript Variables
– Variable:
• A variable is a symbolic name that
represents some data in the memory.
• A variable value can change during the
execution of the JavaScript.
• A variable can be referred by its name
to see or change its value.
• Variables are name are case sensitive.
• Must begin with a letter or underscore.

Rules of a Variable
• Variable Declaration
– Variables can be declared using the var statement
var <variable name>=some value
– Variables can also be created without using var
statement
<variable name>=some value
– Eg
var firstname=“Samuel”
OR
firstname=“Samuel”

Data Type in JavaScript
• JavaScript is a loosely typed language.
• Data Type of Variable
need not be specified
during declaration.
• Data types are
automatically converted
during script execution.
Loosely
Typed??

Data Type in JavaScript (contd.)
• JavaScript recognizes the following type of values:
Values
string
numbers
null
boolean
9, 3.56
true or false
Samuel, ”Samuel J Palmisano”
A Special keyword which refers to
nothing

Data Type in JavaScript (contd.)

JavaScript Operators
Arithmetic Assignment
String
Comparison
Logical
Operators
typeof

JavaScript Operator (contd.)
Arithmetic

Comparison

Assignment

Logical

String

typeof

Flow Control
• Conditional Statements
– if statement - use this statement if you want to
execute some code only if a specified condition is
true.
– if...else statement - use this statement if you want
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 if
you want to select one of many blocks of code to be
executed.
– switch statement - use this statement if you want
to select one of many blocks of code to be
executed.

break and continue Statements
• There are two special statements that can be used
inside loops:
– break.
– continue.
• Break
– The break command will break the loop and continue
executing the code that follows after the loop (if any).
• Continue
– The continue command will break the current loop and
continue with the next value.

Example of break statement
<html>
<body>
var i=0
for (i=0;i<=5;i++)
{ if (i==3){break}
document.write("The number is " + i)
document.write("<br />")
}
</script>
</body>
</html>
Result
The number is 0
The number is 1
The number is 2

Example of continue statement
<html>
<body>
var i=0
for (i=0;i<=5;i++)
{ if (i==3){continue}
document.write("The number is " + i)
document.write("<br />")
}
</script>
</body>
</html>
Result
The number is 0
The number is 1
The number is 2
The number is 4
The number is 5

Functions
• A function is a reusable piece of code that will be
executed when called for.
• A function can be called from anywhere from within the
page or even from other pages if the function is stored
in an external JavaScript (.js) file.
• Functions can be embedded in the <head></head> and
within the<body> </body> tag.

Predefined functions in JavaScript
• DialogBoxes
– alert( message)
Displays an alert box with a
message defined by the
string message.
Eg.
alert(“An Error Occurred!”)

(contd.)
• confirm(message)
– When called, it will display the
message and two boxes. One
box is "OK" and the other is
"Cancel". If OK is selected, a
value of true is returned,
otherwise a value of false is
returned.
Eg.
confirm(“Do you wish to Continue?”)

(contd.)
• prompt(message)
– Displays a box with the message passed to the function
displayed.
– The user can then enter text in the prompt field, and
choose OK or Cancel.
– If the user chooses Cancel, a NULL value is returned. If
the user chooses OK, the string value entered in the
field is returned.
Eg:
prompt(“enter your Name”)

Predefined functions in
JavaScript (contd.)
• Conversion Functions
– eval(string)
Converts a string to an integer or a float value.
Eg
x=“20”
y=eval(x)+10
y contains the value 30

JavaScript (contd.)
– isNaN(value)
If the value passed is not a number then a
boolean value of true is returned else the
boolean value of false is returned.
Eg
x=“Samuel”
y=isNaN(x)
The value stored in y is true

JavaScript (contd.)
– parseInt(string)
Converts a string to an integer returning the first
integer encountered which is contained in the
string.
Eg
x=77AB67
y=parseInt(x)
y stores the value 77

JavaScript (contd.)
– parseFloat(string)
Converts a string to an float value .
Eg
x=77.5AB67
y=parseFloat(x)
y stores the value 77.5

User Defined Functions (contd.)

Common Event Handlers
(contd.)
• onLoad and onUnload
– The onload and onUnload events are triggered
when the user enters or leaves the page.
– The onload event is also triggered when the image
is loaded.
The showstatus() function will be called when a user enters a page
<body onload=“showStatus()”>

(contd.)
• onFocus, onBlur and onChange
– The onFocus, onBlur and onChange events are
often used in combination with validation of form
fields.
The checkEmail() function will be called whenever the user changes the content of the field:
<input type="text" size="30" id="email"
onchange="checkEmail()">;

(contd.)
• onSubmit
– The onSubmit event is used to validate ALL form
fields before submitting it.
The checkForm() function will be called when the user clicks the submit
button in the form.
<form method="post" action="xxx.htm" onsubmit="return checkForm()">

(contd.)
• onMouseOver and onMouseOut
– onMouseOver and onMouseOut are often used to
create "animated" buttons.
An alert box appears when an onMouseOver event is
detected:
<a href="http://www.ibm.com" onmouseover="alert('An
onMouseOver event’)”> <img src=“ibmlogo.gif" width="100"
height="30"> </a>

Example (contd.)
function Addition (x,y) {
var x1=parseInt(x)
var y1=parseInt(y)
var Ans=document.form1.text3.value
var temp=x1+y1
}
<Input type=“text” name=“text3” value=“”>

Example (contd.)
var x1=parseInt(x)
var y1=parseInt(y)
var temp=x1+y1
}
<INPUT TYPE=“button” value=“ +op “
onClick=“Addition(text1.value,text2.value)”>

Example (contd.)
FaaDoOEngineers.com
var x1=parseInt(x)
var y1=parseInt(y)
var temp=x1+y1
if(Ans==temp){
alert(“Your Result agrees with JavaScript!”)
document.form1.text1.value=‘’
}
else{
alert(“No, JavaScript evalutes this operation differently”)
}}
<Form name=“form1” Method=“post” action=“url”
onSubmit=“return validate()>
<Input type=“text” name=“text1” value=“”>

A Complete Program
<html>
<head>
function myfunction(txt)
{
alert(txt)
}
</script>
</head>
<body>
<form>
<input type="button"
onClick="myfunction('Good Morning!')"
value="In the Morning">
onClick="myfunction('Good Evening!')"
value="In the Evening">
</form>
<p>
When you click on one of the buttons, a
function will be called. The function will
alert
the argument that is passed to it.
</p>
</body>
</html>

myfunction (txt) receives “ Good
Morning!”

myfunction (txt) receives “ Good
Evening !”

JavaScript Objects
• JavaScript is not a true Object Oriented language as
C++ or Java but rather an Object Based language.
• Objects in JavaScript are software entities such as the
browser window or an HTML document.

Instances of Computer Objects
(contd.)

Document Object Model
• The DOM is a programming API for documents.
• It is based on an object structure that closely resembles the
structure of the documents it models.
• For instance, consider this table, taken from an HTML
document:
<TABLE>
<TBODY>
<TR> <TD>Shady Grove</TD> <TD>Aeolian</TD> </TR>
<TR> <TD>Over the River, Charlie</TD> <TD>Dorian</TD>
</TR>
</TBODY>
</TABLE>

Graphical representation of the DOM of the example table
Document Object Model (contd.)

• With JavaScript you can restructure an entire HTML
document. You can add, remove, change, or reorder
items on a page.
• To change anything on a page, JavaScript needs
access to all elements in the HTML document. This
access, along with methods and properties to add,
move, change, or remove HTML elements, is given
through the Document Object Model (DOM).

Document Tree

How to access the nodes in an
HTML
• You can find the element you want to manipulate in
several ways:
– By using the getElementById() and
getElementsByTagName() methods
– By using the parentNode, firstChild, and lastChild
properties of an element node

Navigator Object
• Navigator object is the object representation of the
client internet browser or web navigator program that is
being used.
• This is a top level object to all others object in DOM
hierarchy.

Navigator Object Properties
• appCodeName – The name of the browser’s code
such as Internet Explorer
• appName – The name of the browser.
• appVersion – The version of the browser.
• plugins – An array of plug-ins supported by the
browser and installed on the browser.
• cpuClass – The type of CPU which may be “x86”.
• cookieEnabled – A boolean value of true or false
depending on whether cookies are enabled in the
browser.

Navigator Object Methods
• javaEnabled() – Returns a boolean telling if the
browser has JavaScript enabled.

Window Object
• The Window object is 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> tag.

Window Object Properties
• name – sets of return the name of the window.
• statusbar - sets whether or not the browser’s statusbar
should be visible.
• toolbar - sets whether or not the browser’s toolbar
should be visible.
• document
• history

Window Object Methods
• open() – Opens a new browser window.
• createPopup() – Creates a popup window.
• setInterval(code,millisec[,lang]) – Evaluates an
expression at specified intervals.
• focus() – sets the focus to the current window.
• blur() – removes focus from the current window.
• close() – closes the current window.

Document Object
• The document object represents the entire HTML
document and can be used to access all elements in a
page.
• The document object is part of the window object and is
accessed through the window.document property or
simply document.

Document Object Collections
• anchors[] - Returns a reference to all Anchor objects in
the document.
• forms[] - Returns a reference to all Form objects in the
document.
• images[] - Returns a reference to all Image objects in
the document.
• links[] - Returns a reference to all Area and Link objects
in the document.

Document Object Properties
• Body – gives direct access to the <body> element.
• Cookie – Sets or returns all cookies associated with the
current document.
• lastModified – Returns the date and time a document
was last modified.
• Title – Returns the title of the current document.
• URL – Returns the URL of the current document.

Document Object Methods
• write() - Writes HTML expressions or JavaScript code
to a document
• getElementByID() – Returns a reference to the first
object with the specified id.
• getElementsByName() – Returns a collection of
objects with the specified name.
• getElementsByTagName() – Return a collection of
objects with the specified tag name.

History Object
• History object is a JavaScript object.
• The History object is automatically created by the
JavaScript runtime engine and consists of and array of
URLs.
• It is a part of window object & accessed through
window.history property.

Cookies
• A cookie can store a small amount of information about
a user visiting a site.
• A cookie is a small text file that is stored on the site
visitor's computer by their browser .
• Because the cookie is stored on the user’s computer, it
does not require any server space no matter how many
users you have .
• With JavaScript, you can both create and retrieve
cookie values.

Cookies (contd.)
• You can use cookies to :
– save user preferences.
– customize data.
– remember the last visit.
– Keep track of items in an order while a user
browses.
– Remember the information your site’s visitors gave
last time.
• Cookies can be created, read and erased by
JavaScript. They are accessible through the property
document.cookie

Cookies (contd.)
• What does a cookie contain?
– Name value pair
• The first element in a cookie is a "name"
attribute, followed by the data to be stored in the
cookie.
– The expiry date
• specifies how long the cookie is valid for.

Cookies (contd.)
• What does a cookie contain?
– The path
• this states where the cookie may be accessed
from on the Web site. Most often, this is set to
the server's document root.
– The domain
• The "domain" attribute allows you to set a
domain name for the cookie. Again, this is
optional.

Format of Cookie
• First the name value pair.
• Then a semicolon and a space.
• Then the expiry date.
– Expiry date should be in UTC format.
• Then again a semicolon and a space.
• Then the path.

Format of Cookie (contd.)
• document.cookie=<name of cookie>=<value of
cookie>;<blank space>expires=<date in UTC
format>;<blank space>path=<path location>
Example
document.cookie = ‘user=Mujtaba; expires=Fri, 30 April 2021 20:47:11 UTC;
path=/'

Example of Setting a Cookie
<html>
<head>
<script language="JavaScript">
function setCookie(name, value) {
var exp=new Date(“April 30,2021")
document.cookie=name+"="+escape
(value)+"; expires="+exp.toGMTString() +"; path=/“
document.write(“Cookie has been set”)
) </script>
</head>
<body>
<form>
value="Set a Cookie"
onClick="setCookie(‘user',‘
Paul Smith')">
</form>
</body>
</html>
Set an expiry date
What does the
escape function
do?

escape() function
• There's no escape!
– Strictly speaking, we should be escaping our cookie
values -- encoding non-alphanumeric characters
such as spaces and semicolons.
– This is to ensure that our browser can interpret the
values properly.
– Fortunately this is easy to do with JavaScript's
escape() function.
For example
document.cookie = "username=" + escape(“Paul
Smith") + "; expires=15/02/2003 00:00:00";

Example of Setting a Cookie
<html>
<head>
function setCookie(name, value) {
var exp=new Date(“April 30,2021")
document.cookie=name+"="+escape
(value)+"; expires="+exp.toGMTString() +"; path=/“
document.write(“Cookie has been set”)
)
</script>
</head>
<body>
<form>
<input type="button" value="Set a
Cookie"
onClick="setCookie(‘user',‘Mujtaba')"
>
</form>
</body>
</html>
Setting the cookie
The value stored is
user=Mujtaba

Reading a Cookie
<html>
<head>
function readCookie() {
var ca = document.cookie
document.write(ca)
}
</script>
</head>
<body>
<form><input type="button"
value="read"
onClick="readCookie()">
</form>
</body>
</html>
Returns the cookie
name value pair
Value retrieved is
user=Mujtaba

Extracting only the value from
the Cookie
<html>
<head>
function readCookie(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
document.write(
document.cookie.substring(c_
start,c_end))
}
}
}
</script>
</head>
<body>
<form> <input type="button"
value="read"
onClick="readCookie('user')">
</form>
</body>
</html>
Displays the value:
Mujtaba

Delete Cookies
<html>
<head>
function deleteCookie ( cookie_name)
{
var cookie_date = new Date ( )
cookie_date.setTime ( cookie_date.getTime() - 1 )
document.cookie = cookie_name += "=; expires=" +
cookie_date.toGMTString()
}
</script>
</head>
<body>
<form>
value=“delete"
onClick="deleteCookie(‘
user')">
</form>
</body>
</html>
The cookie's expiry date is set
to one second less then the
current date.

Modifying a cookie
• To modify a cookie simply reset the values and use the
same procedure for setting the cookie.
• Ensure that the cookie name is existing or a new
cookie will be created.

Lecture 5 javascript

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