Creating a Programmable Web Page - Introduction to Java Script - Lecture Slides, Slides of Javascript programming

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JavaScript

Creating a Programmable Web Page

Tutorial Objectives

• Understand basic JavaScript syntax
• Create an embedded and external script
• Work with variables and data
• Work with data objects and extract values from dates
• Work with expressions and operators
• Create and call a JavaScript function
• Work with arrays and conditional statements
• Learn about program loops

Server-Side Programs

• a user must be connected to the Web server to run

the server-side script

• only the programmer can create or alter the script
• the system administrator has to be concerned about

users continually accessing the server and potentially

overloading the system

Client-Side Programs

• solve many of the problems associated with server-side

scripts

• can be tested locally without first uploading it to a Web

server

• are likely to be more responsive to the user
• can never completely replace server-side scripts

Introduction to JavaScript

• JavaScript is an interpreted programming or script language from Netscape.
• JavaScript is used in Web site development to such things as:

 automatically change a formatted date on a Web page

 cause a linked-to-page to appear in a popup window  cause text or a graphic image to change during a mouse rollover

Java vs. JavaScript

• Requires the JDK to create the applet
• Requires a Java virtual machine to run the applet
• Applet files are distinct from the XHTML code
• Source code is hidden from the user
• Programs must be saved as separate files and compiled before they can be run
• Programs run on the server side
  • Requires a text editor
  • Required a browser that can interpret JavaScript code
  • JavaScript can be placed within HTML and XHTML
  • Source code is made accessible to the user
  • Programs cannot write content to the hard disk
  • Programs run on the client side

ECMAScript

• The responsibility for the development of a scripting

standard has been transferred to an international body

called the European Computer Manufacturers Association

(ECMA).

• The standard developed by the ECMA is called

ECMAScript, though browsers still refer to it as JavaScript.

• The latest version is ECMA-262, which is supported by the

major browsers.

Other Client-side Languages

• Internet Explorer supports JScript.
• JScript is identical to JavaScript, but there are some

JavaScript commands not supported in JScript, and vice

versa.

• Other client-side programming languages are also

available to Web page designers, such as the Internet

Explorer scripting language, VBScript.

Example of Web Site using JavaScript

Writing a JavaScript Program

• The Web browser runs a JavaScript program when the Web page is first loaded, or in response to an event.
• JavaScript programs can either be placed directly into the HTML file or they can be saved in external files. - placing a program in an external file allows you to hide the program code from the user - source code placed directly in the HTML file can be viewed by anyone

Writing a JavaScript Program

• A JavaScript program can be placed anywhere within the HTML file.
• Many programmers favor placing their programs between tags in order to separate the programming code from the Web page content and layout.
• Some programmers prefer placing programs within the body of the Web page at the location where the program output is generated and displayed.

Using the

• To access an external script, use:

<script src=“ url ” type=“text/javascript”>

script commands and comments

Comments

• The syntax for a single-line comment is:

// comment text

• The syntax of a multi-line comment is:

/*

comment text covering several lines

*/

Hiding Script from Older Browsers

• You can hide the script from these browsers using comment tags:
• When a Web browser that doesn’t support scripts encounters this code, it ignores the