JavaScript
Table of Contents
1.1 Introduction
1.2 Functions and Events
1.3 JavaScript Code
1.4 JavaScript Variables
1.5 Arithmetic and Assignment Operators
1.6 Comparison Operators
1.7 Logical Operators
1.8 Conditional Operator
1.9 Conditional Statements
1.10 POP UP Box
1.11 JavaScript Functions
1.12 JavaScript Loops
1.13 Events
1.14 JavaScript - Catching Errors
1.15 JavaScript Objects Introduction
JavaScript
1.1 Introduction
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.
1.1.1 What is JavaScript?
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++.1.1.2 Characteristics of JavaScript
• 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 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
1.1.3 JavaScript and ECMAScript Language Standard
• JavaScript is an implementation of the ECMAScript language standard. ECMA-262 is the official
JavaScript standard.
• JavaScript was invented by Brendan Eich at Netscape (with Navigator 2.0), and has appeared in
all browsers since 1996.
• The official standardization was adopted by the ECMA organization (an industry standardization
association) in 1997.
• The ECMA standard (called ECMAScript-262) was approved as an international ISO (ISO/IEC
16262) standard in 1998.
• The development is still in progress.
• The HTML <script> tag is used to insert a JavaScript into an HTML page.
1.1.4 Writing to the HTML Document
The example below writes a <p> element with current date information to the HTML document:<html>
<body>
<h1> My First Web Page </h1>
<script type="text/Javascript's">
document.write ("<p>)"+ Date() +("</p>");
</script>
</body>
</html>
Note: Try to avoid using document.write() in real life JavaScript code. The entire HTML page will be overwritten if document.write() is used inside a function, or after the page is loaded.
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