Chapter 14 - Web Design

Copyright © Terry Felke-Morris
WEB DEVELOPMENT & DESIGN
FOUNDATIONS WITH HTML5
Chapter 14
Key Concepts
1Copyright © Terry Felke-Morris

LEARNING OUTCOMES
 In this chapter, you will learn how to:
 Describe common uses of JavaScript in web pages.
 Describe the purpose of the Document Object Model
and list some common events.
 Create a simple JavaScript using the script element and
the alert() method.
 Use variables, operators and the if control structure.
 Create a basic form validation script.
2

WHAT IS JAVASCRIPT?
 Object-based scripting language
 Works with the objects associated with a
Wwb page document
 the window
 the document
 the elements
 such as forms, images, hyperlinks, etc
3

WHAT IS JAVASCRIPT?
 Originally developed by Netscape
 Named LiveScript
 Netscape & Sun Microsystems Collaboration
 LiveScript renamed JavaScript
 JavaScript is NOT Java
4

COMMON USES OF JAVASCRIPT
 Display a message box
 Select list navigation
 Edit and validate form information
 Create a new window with a specified size and
screen position
 Image Rollovers
 Status Messages
 Display Current Date
 Calculations
5

CODING JAVASCRIPT
 JavaScript statements can be coded on a web page
using two different techniques:
 Place JavaScript code between <script> tags
 Place JavaScript code as part of an event attached to an
HTML element
6

JAVASCRIPT: USING THE SCRIPT ELEMENT
The script element
◦ A container tag
◦ May be placed in either the head or the body
section of a web page
<script type="text/javascript">
<!- -
alert("Welcome to Our Site");
// - ->
</script>
7

CHECKPOINT
1. Describe at least three popular uses for
JavaScript.
2. How many JavaScript code blocks can be
embedded in an HTML document?
3. Describe a method that can be used to find an
error in a JavaScript code block.
8

DOCUMENT OBJECT MODEL (DOM)
A portion of the
DOM is shown at the
left.
Defines every object
and element on a web
page
Hierarchical structure
Accesses page
elements and apply
styles to page
elements
9

OBJECT
 An object is a thing or entity.
 Browser window
 Submit button
 Web page document
10

PROPERTY
 A property is a characteristic or attribute of an
object.
 The background color of a web page document
document.bgcolor
 The date the web page file was last modified
document.lastmodified
 The src file of an image object
image1.src
11

METHOD
 A method is an action (a verb)
 Writing text to a web page document
document.write()
 Submitting a form
form1.submit()
12

JAVASCRIPT AND EVENTS
Events:
actions taken by the web page visitor
◦ clicking (onclick),
◦ placing the mouse on an element (onmouseover),
◦ removing the mouse from an element (onmouseout),
◦ loading the page (onload),
◦ unloading the page (onunload), etc.
13

EVENTS
Event Event Handler
click onclick
load onload
mouseover onmouseover
mouseout onmouseout
submit onsubmit
unload onunload
14

JAVASCRIPT AND EVENTS
 JavaScript can be configured to perform actions when
events occur.
 The event name is coded as an attribute of an HTML tag
 The value of the event attribute contains the JavaScript code
Example:
Display an alert box when the mouse is placed over a
hyperlink.
15
<a href="home.htm" onmouseover="alert('Click to go home')">Home</a>

JAVASCRIPT DEBUGGING(1)
Check the syntax of the statements
◦ Pay very close attention to upper and lower case letters, spaces, and quotations
Verify that you have saved the page with your most recent changes
Verify that you are testing the most recent version of the page
(refresh or reload the page)
If you get an error message, use the error messages that are
displayed by the browser
◦ In Firefox: Select Tools > Error Console
16

JAVASCRIPT DEBUGGING(2)
 Use the Firefox browser:
 Select Tools > Error Console from the Menu
 The Error Console will indicate an issue and the line number
 This may not be exactly where the problem is
 Sometimes the error is a one or two lines above the indicated line
number.
17

CHECKPOINT
1. With respect to objects, describe the difference between a
property and a method. Feel free to use words like “thing,”
“action,”“description,”“attribute,” and so forth.
2. What is the difference between an event and an event
handler?
3. Where are event handlers placed in the HTML document?
18

VARIABLE
 A variable is a placeholder for information.
 The variable is stored in the computer’s memory
(RAM).
var userName;
userName = "Karen";
document.write(userName);
19

PROMPTS
 prompt() method
 Displays a message and accepts a value from the user
myName = prompt(“prompt message”);
 The value typed by the user is stored in the variable
myName
20

ARITHMETIC OPERATORS
Operat
or
Description Example Value of
Quantity
= assign quantity = 10 10
+ addition quantity = 10 + 6 16
- subtraction quantity = 10 - 6 4
* multiplication quantity = 10 * 2 20
/ division quantity = 10 / 2 5
21

COMPARISON OPERATORS
Operator Description Example Sample values of quantity
that would result in true
= = Double equals
sign
(equivalent)
“is exactly
equal to”
quantity = = 10 10
> Greater than quantity > 10 11, 12 (but not 10)
> = Greater than
or equal to
quantity > = 10 10, 11, 12
< Less than quantity < 10 8, 9 (but not 10)
< = Less than or
equal to
quantity < = 10 8, 9, 10
! = Not equal to quantity ! = 10 8, 9, 11 (but not 10)
22

DECISION MAKING
if (condition) {
… commands to execute if condition is true
}
else {
… commands to execute if condition is false
}
23

FUNCTION
 A function is a block of one or more JavaScript
statements with a specific purpose, which can be
run when needed.
function function_name() {
... JavaScript statements …
}
24

USING FUNCTIONS
function showAlert() {
alert("Please click OK to continue.");
}
25
Calling the Function
showAlert();
Defining the Function

CHECKPOINT
1. Describe a method that can be used to gather a piece of data such as
the user’s age.
2. Write the JavaScript code to display an alert message for users who
are under 18 years old and a different alert message for users who
are 18 years or older.
3. What is a function definition?
26

FORMVALIDATION
 It is common to use JavaScript to validate form
information before submitting it to the web server.
 Is the name entered?
 Is the e-mail address of correct format?
 Is the phone number in the correct format?
 See Hands-on Practice 14.8
27

VALIDATING FORM FIELDS
 Use the "" or null to check to determine if a
form field has information
if (document.forms[0].userName.value == "" ) {
alert("Name field cannot be empty.");
return false;
} // end if
28

JAVASCRIPT & ACCESSIBILITY
 Don’t expect JavaScript to always function for
every visitor
 Some may have JavaScript disabled
 Some may be physically unable to click a mouse
 Provide a way for your site to be used if JavaScript
is not functioning
 Plain text links
 E-mail contact info
29

CHECKPOINT
1. What is meant by the term “form data validation”?
2. Give three examples of form data that may require
validation.
3. Should you always expect your JavaScript to “work” –
why or why not?
30

SUMMARY
This chapter introduced the use of JavaScript on
web pages.
Topics included:
 Common uses of JavaScript in web pages.
 The purpose of the Document Object Model
 The script element
 The alert() method
 Use variables, operators and the if control structure.
 Configure functions
 Using JavaScript to validate a form
31

Chapter 14 - Web Design

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Chapter 14 - Web Design