JavaScript for Beginners - Basic Concepts (Variables) (P: V)

Variables

Variables are containers for sorting data values. The value of a variable can change throughout the program.

In JavaScript use the var keyword to declare a variable:

In the example above, the variable x is assigned the value 10.

Note: JavaScript is case sensitive. For example, the variables lastName and lastname, are two different variables.

The Equal Sign

In JavaScript, the equal sign (=) is called the “assignment” operator, rather than an “equal to” operator.

For example, x = y will assign the value of y to x.

Let’s assign a value to a variable and output it to the browser

Result:

 

Note: A variable can be declared without a value. The value might require some calculation, something that will be provided later, like user input.

A variable declared without a value will have the value undefined

Using variable is useful in many ways. You might have a thousand lines of code that may include the variable x. When you change the value of x one time, it will automatically be changed in all places where you used it

Note: Every written “instruction” is called a statement. JavaScript statements are separated by semicolons.

Naming Variables

Here are some naming rules for JavaScript variables

-          The first character must be a latter, an underscore (_), or a dollar sign ($). Subsequent characters may be letters, digits, underscores, or dollar signs.

-          Numbers are not allowed as the first character

-          Variable names cannot include a mathematical or logical operator in the name.

-          JavaScript names must not contain spaces.

There are some other rules to follow when naming your JavaScript variables.

-          You must not use any special symbols, like my#num, num%, etc.

-          Be sure that you do not use of the following JavaScript reserved words

Reserved Words in JavaScript
abstract	else	instanceof	switch
boolean	enum	int	synchronized
break	export	interface	this
byte	extends	long	throw
case	false	native	throws
catch	final	new	transient
char	finally	null	true
class	float	package	try
const	for	private	typeof
continue	function	protected	var
debugger	goto	public	void
default	if	return	volatile
delete	implements	short	while
do	import	static	with
double	in	super

Note: When you get more familiar with JavaScript remembering these keywords will be much easier.

Hyphens are not allowed in JavaScript. It is reserved for subtraction.