project 1: using javascript essentials for design javascript level one michael brooks

Project 1: Using JavaScript

Essentials for DesignJavaScript

Level OneMichael Brooks

Copyright (c) 2004 Prentice-Hall. All rights reserved. 2

Objectives

Integrate JavaScript into HTML documents

Use inline JavaScript within HTML tags

Create simple functions

Insert programmer's comments into JavaScript source code


Objectives (continued)

Hide JavaScript code from incompatible browsers

Display alternate content in non-compatible browsers


Why Would I Do This?

The JavaScript language was created to overcome the limitations of HTML HTML is a simple scripting language that tells a

Web browser how to display a Web page Netscape developed the LiveScript language

for use in its Netscape Navigator Web browser LiveScript’s name was changed to JavaScript with

the release of Navigator 2.0 Java and JavaScript are distinct languages

and should not be confused

dean atchison

This slide is too text heavy. Neither the learner nor the teacher want to reread the text while viewing or lecturing with the slides.The slides should contain about 4-5 lines of text with about 4-5 words per line.There is no image.


Why Would I Do This? (continued) Microsoft developed its own version of

JavaScript in Internet Explorer 4.0 called Jscript

The differences between JScript and JavaScript created problems for Web developers

The European Computer Manufacturers Association (ECMA) developed a standardized version of JavaScript, which became known as ECMAScript


Why Would I Do This? (continued) JavaScript:

Allows users to interact with Web pages

Allows developers to:

create content based on user choices

take greater control over the Web browser

Can be used for a number of common applications


Why Would I Do This? (continued) JavaScript common

applications include:

Creating a rollover, such as a button graphic, that changes when the user rolls the mouse over it

Validating the content of a field in a form

Computing a calculation


Why Would I Do This? (continued) Creating a pop-up

window to display an ad

Creating animation using a combination of JavaScript and other technologies, such as Cascading Style Sheets (CSS)


Visual Summary JavaScript was designed to

enhance HTML, not to replace it

JavaScript is often used in HTML documents by simply using the <script> tag The <script> tag is an HTML

tag created to allow the incorporation of other scripting languages within HTML pages


Visual Summary (continued)

The file name is identified at the top of the window in the main Menu bar

The <SCRIPT> tag allows JavaScript to be inserted into an HTML document

The language attribute specifies the scripting language that appears within the HTML

Browsers often support a variety of different scripting languages, but JavaScript is the most popular



The <script> tag allows JavaScript to be inserted into an HTML document

The language attribute

The file name

HTML code with added JavaScript



HTML code with added JavaScript displayed in a browser window

The user must acknowledge the message, by clicking on the OK button, to continue

An alert box is generated by the alert() method


Incorporating JavaScript into an HTML JavaScript is a scripting language

A scripting language: is similar to a traditional programming language is usually less powerful and often designed for

a specific function In JavaScript’s case, that specific function is

making Web pages more interactive


Incorporating JavaScript into an HTML (continued) When you view a Web page in a browser, an

interpreter decides how to display the HTML or JavaScript code, and then returns information to the screen This process is known as parsing


Incorporating JavaScript into an HTML (continued) JavaScript is primarily used for client-side

scripting Web browser usually interprets JavaScript code

Server-side scripting means the Web server processes the script instead of the user’s computer Requires more computer resources Is often necessary for tasks that require secure

information, such as processing a credit card transaction


Incorporating JavaScript into an HTML (continued) Common languages used for server-side

scripting include ASP, Java, Visual Basic, and PHP


Incorporating JavaScript into an HTML (continued) JavaScript is simply text that is interpreted by

the browser when it is encountered You can use JavaScript in Web sites in

several ways: Embedding code between the HTML <script> and

</script> tags<script language="JavaScript">function triggerAlert() { alert("function is activated"); }</script>

Embeddedcode


Incorporating JavaScript into an HTML (continued)

Using inline code within HTML code Inline code usually means that a single JavaScript

command appears inside an HTML tag Typically, this command is associated with an event,

such as when someone clicks on a hyperlink

<body onLoad="alert(’Welcome to my Web site!’);">

Inline code



Defining code within the <head> section of an HTML document as a function that can be called upon within the body of the HTML document

<head><script language="JavaScript">function triggerAlert() { alert("function is activated"); }</script></head>

JavaScript code at the top of the HTML



Storing JavaScript code in an external file that can be linked to the HTML document This method offers a powerful way to share JavaScript

code between multiple documents Example of storing JavaScript code in an external

file that can be linked to the HTML document



Methods JavaScript commands

follow a specific syntax that is stricter than HTML

Commands that perform actions are called methods

A method is always written with parentheses, such as alert()



Methods may need additional information to perform a specific action

When sending information, such as a text message, quotations are used to mark the beginning and ending of the text



The alert() method

Additional information sent to the alert() method to perform a specific action

An example of using the JavaScript alert() method


Incorporating JavaScript into an HTML (continued) Scripting Versus Programming Languages

Traditional programming languages are converted to “machine code” that can only be read by the intended type of machine (they are platform specific)

Scripting languages are interpreted (parsed) by the software that reads them

The result of this difference is that scripting languages usually run slower, but can be used on different hardware platforms (they are platform independent)

Scripting languages also have built-in security features that keep developers from building harmful or malicious code that could harm a Web surfer’s


Using Inline JavaScript

Inline JavaScript refers to JavaScript code that is used within an HTML tag

Inline JavaScript appears within quotes, the same as HTML tag attributes

With inline JavaScript, you do not use the <script> tag

<body onLoad="alert('Welcome to my Web site!');">

Including an Inline JavaScript


Using Inline JavaScript (continued) Inline JavaScript is triggered by an event,

which is an action the user performs, such as clicking an image or a button An event handler is a keyword (a word that has

a meaning in the language used) that allows the computer to detect an event

JavaScript event handlers can appear as HTML tag attributes or properties

The event handler tells JavaScript when to carry out a command


Using Inline JavaScript (continued)

In the above example, the alert() command is activated when the mouse is clicked (onClick)

The Event Handler



In the above example, the alert() command is activated when the mouse is clicked (onClick) on the image

<img src="TIGER.JPG" onClick=" triggerAlertTiger();">

dean atchison

this is a good slide . . . clean, simple, just reduce the number of alignments to unify the items.this slide is not text heavystill don't need to type sentences



The above example shows an event handler to the <body> tag as inline JavaScript (Internet browser display of this example)

The Event Handler


Using Inline JavaScript (continued) Functions

Functions are named, reusable sections of code that can exist in the head or body section of an HTML document, or in an external file

Functions allow developers to reuse code without having to retype it every time it is needed

When you place a function in an external file, it can be shared between all the documents in a Web site

Information can be sent to a function and a function can send information back to other scripts or other functions



The keyword function is used to create a reusable, named section of code

Functions are typically triggered by event handlers using inline code that appear as an HTML tag attribute



In the example above, the function is triggered when the user clicks on the image

The function triggerAlert()

The function triggerAlert() is triggered by the onclick event handlers


Programmer's Comments

Programmer’s comments

Programmer’s comments are messages that programmers insert directly into their source code to explain how the code was written

Programmer’s comments are invisible to end users who view the page in the browser, and they are ignored by the JavaScript interpreter


Programmer's Comments (continued)

The browser does not display any information contained in a JavaScript comment

This keeps the text created by the second document writeln() command from appearing in the browser window

<html><head></head><body><script language=”JavaScript”>//this page outputs text to the windowdocument.write(“Hello”);/* document.write(“How are you?”); */</script></body></html>Comments not shown in the

browser window


Hide JavaScript Code from Incompatible Browsers

Newer versions of the most commonly used browsers can all interpret comments correctly

Older versions of IE, Navigator, and other browsers, however, cannot interpret the comments Many times, this results in the comments being

displayed in the browser window


Hide JavaScript Code from Incompatible Browsers (continued) The workaround for this problem is: combining

programmer’s comments with HTML comment tags to hide JavaScript code from browsers that cannot interpret the <script> tag or the scripting language contained between the <script> and </script> tags

Example


Hide JavaScript Code from Incompatible Browsers (continued) The <No-script> Tag

The <noscript> tag allows you to create content that will only display in browsers that cannot display the <script> tag

Even if most modern browsers usually support the <script>, it is considered good form to be prepared for the rare circumstance when a particular browser does not support the feature by always including the <noscript> tag


Hide JavaScript Code from Incompatible Browsers (continued)

Example of using the <No-script> tag

The text contained between the <NOSCRIPT> pair tags will only display in browsers that cannot display the <script> tag



By default, most browsers are configured to ignore errors generated by scripting languages such as JavaScript

To view errors that are generated by scripting languages, you can turn on the error notifications feature

<html><head><title>comments.html</title></head><body><script language="JavaScript"></script><noscript>Your browser doesn’t support JavaScript or JavaScript is disabled. JavaScript is required to view this page correctly. </noscript></body></html>

IE browser Error Notification


Case Sensitivity

Case sensitivity refers to a language’s ability to distinguish between uppercase (capital) and lowercase (small) letters

Languages that distinguish between uppercase and lowercase letters are said to be case sensitive

A case-sensitive program that expects you to enter all commands in uppercase will not respond correctly if you enter one or more characters in lowercase


Case Sensitivity (continued)

JavaScript is a case-sensitive language It is different than HTML, which ignores

differences between upper-and lowercase letters

Users must be aware of the proper spelling of JavaScript commands

Errors in case often cause difficult-to-find problems in JavaScript code

<html><head><title>comments.html</title></head><body><script language="JavaScript"></script><noscript>Your browser doesn’t support JavaScript or JavaScript is disabled. JavaScript is required to view this page correctly. </noscript></body></html>

Since line 7 contains an error: “Document” should start with lower case “d”, depending on which browser you are using and how it is configured, the JavaScript interpreter may display an error message



Error shown in the Internet Explorer browser



Event handlers used in HTML commands aren’t case sensitive because they appear as HTML attributes

Some browsers ignore some case mistakes in JavaScript code and this often creates problems since the developer doesn’t notice the error until the code is tested in another browser

project 1: using javascript essentials for design javascript level one michael brooks

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