JavaScript Introduction

JavaScript is one of the most popular programming languages on the web. It is used in millions of web pages to add functionality, validate forms, detect browsers, and much more.

What is JavaScript?

JavaScript is...

• a scripting language
  (lightweight programming language)
• an interpreted language (not compiled)
• an Object Oriented Programming (OOP) language
• usually embedded directly into HTML pages
• available in all major browsers, such as Firefox, Internet Explorer, Chrome, Opera, and Safari
• NOT Java

JavaScript can be used to make web pages dynamic, react to events, validate data, create cookies, and detect browser information.

JavaScript Tips & Guidelines

The following are important things to know when coding with JavaScript.

Case Sensitivity

JavaScript is case sensitive - therefore ensure the capitalization is correct for variable and function names. A variable named "myIndex" is not the same as "myindex".

Semicolons

Although the JavaScript interpreter automatically adds semicolons to the end of most lines, it is a best practice to add them when writing JavaScript to avoid strange side effects when the interpreter does it automatically.

Whitespace and New Lines

Most whitespace such as spaces, tabs, and empty lines is ignored by the JavaScript interpreter. In general, it is best to use whitespace when coding JavaScript to aid readability.

// These lines are equivalent
x="String";
x = "String";

Breaking a Line of Code

Long lines of code can be broken up with a backslash character as long it is within a text string.

document.write("Hello \
from JavaScript");

Reserved Words

JavaScript reserves certain words for specific uses. The following table lists the JavaScript reserved words:

break	case	catch
continue	default	delete
do	else	finally
for	function	if
in	instanceof	new
return	switch	this
throw	try	typeof
var	void	while
with

The following table lists the reserved for future keywords by the ECMAScript specification:

abstract	boolean	byte
char	class	const
debugger	double	enum
export	extends	final
float	goto	implements
import	int	interface
long	native	package
private	protected	public
short	static	super
synchonized	throws	transient
volatile

In addition to the ECMAScript reserved words, certain JavaScript-specific words implemented in most browsers are considered reserved by implementation. The following table lists these reserved keywords:

arguments	Array
Boolean	Date
decodeURI	decodeURIComponent
encodeURI	Error
escape	eval
EvalError	Function
Infinity	isFinite
Math	NaN
Number	Object
parseFloat	parseInt
RangeError	ReferenceError
RegExp	String
SyntaxError	TypeError
undefined	unescape
URIError

JavaScript Statistics