JavaScript Introduction

JavaScript is the most popular scripting language on the internet, and works in all major browsers, such as Internet Explorer, Firefox, Chrome, Opera, and Safari.

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What You Should Already Know

Before you continue you should have a basic understanding of the following:

• HTML and CSS

If you want to study these subjects first, find the tutorials on our Home page.

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What is JavaScript?

• 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

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Are Java and JavaScript the same?

NO!
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++.

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What Can JavaScript do?

• 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 manipulate 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 input
• 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

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JavaScript = ECMAScript

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.

JavaScript Array Object

What is an Array?

An array is a special variable, which can hold more than one value, at a time.
If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:

var car1="Saab";
var car2="Volvo";
var car3="BMW";

However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?
The best solution here is to use an array!
An array can hold all your variable values under a single name. And you can access the values by referring to the array name.
Each element in the array has its own ID so that it can be easily accessed.

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Create an Array

An array can be defined in three ways.
The following code creates an Array object called myCars:
1:

var myCars=new Array(); // regular array (add an optional integer
myCars[0]="Saab";       // argument to control array's size)
myCars[1]="Volvo";
myCars[2]="BMW";

2:

var myCars=new Array("Saab","Volvo","BMW"); // condensed array

3:

var myCars=["Saab","Volvo","BMW"]; // literal array

Note: If you specify numbers or true/false values inside the array then the variable type will be Number or Boolean, instead of String.

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Access an Array

You can refer to a particular element in an array by referring to the name of the array and the index number. The index number starts at 0.
The following code line:

document.write(myCars[0]);

will result in the following output:

Saab

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Modify Values in an Array

To modify a value in an existing array, just add a new value to the array with a specified index number:

myCars[0]="Opel";

Now, the following code line:

document.write(myCars[0]);

will result in the following output:

Opel

How to detect Render Mode of browser for current page?

Before IE8:

alert('Page was rendered in ' +
  ((document.compatMode == 'CSS1Compat') ? 'Standards' : 'Quirks') + ' Mode.');

For IE8:

var vMode = document.documentMode;
var rMode = 'IE5 Quirks Mode';
if(vMode == 8){
  rMode = 'IE8 Standards Mode';
} else if(vMode == 7){
  rMode = 'IE7 Strict Mode';
}
alert('Rendering in: ' + rMode);