Variables in JavaScript

Variables are used for storing data value. JavaScript variables are container (Placeholder)

 for storing value. a variable an have different phases for execution.  And global variable.

 Since the content of a variable varies throughout the execution of a program, they are

 called variable.

 

Declaring JavaScript variables

Creating variable in any programming language is called “declaring” a variable.

 JavaScript variable can be declared with the var keyword. 

There are some rules while declaring a JavaScript variable (also known as identifiers).

1. Name must start with a letter (a to z or A to Z), underscore (_), or dollar ($) sign.

2. After first letter we can use digits (0 to 9), for example value1.

3. JavaScript variables are case sensitive, for example x and X are different variables.

 

Ex1.

In below Example, variable var1 is defined with initial value of 100 where variable

var2 is defined without any initial value.

 

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Ex2.a,b ,and sum, are variables-

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JavaScript Variable Scope

The scope of a variable is the region of your program in which it is defined. A JavaScript

 variable is simply a name of storage location. JavaScript variables have only two

 scopes.

 

JavaScript local variable

A JavaScript local variable is declared inside block or function. It is accessible within the

 function or block only. For example:

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JavaScript global variable

A JavaScript global variable is accessible from any function. A variable i.e. declared

 outside the function or declared with window object is known as global variable.

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Declaring JavaScript global variable within function

To declare JavaScript global variables inside function, you need to use window object. 

Automatically Global Variable

When a variable used for the first time inside a function, is assigned a value without declaring (using var).will become global automatically.

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Local Variables are deleted when function is completed where as global variable are deleted when page execution is completed. Argument is always local.

 

Note:- JavaScript  variable are loosely-typed which means it does not require a data type to be declared like other programming language .you can assign any type of literal values to a variable e.g. string, integer, float, Boolean etc.

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JavaScript Reserved Words

A list of all the reserved words in JavaScript is given in the following table. They cannot

 be used as JavaScript variables, functions, methods, loop labels, or any object names.

 

abstract	else	instance of	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
double	in	super

Declare multiple Variables in JavaScript

 

In this article, we will see how to declare multiple Variables in JavaScript. The

Variables can be declared using var, let, and const keywords. Variables are

Containers that store some value and they can be of any type.

These are the following ways to declare multiple variables:

 

Table of Content

 

1) Declaring Variables Individually

 

2) Declaring Variables in a Single Line

 

3) Using Restructuring Assignment

 

Data Types in Java Script

Data Type is used to define what type of data can be stored and manipulated with in a 

program. There two types of data type sin JavaScript.

 

Primitive Data Type

String-

It represents sequence of e.g. “AD Computer Campus”.

Number-

It represents numeric values (integer, float, hexadecimal, octal, and exponential

Boolean-

It represents Boolean Value either false or true.

Undefined-

It represents undefined value.

NULL-

It represents null i.e. no value at all.

 

Non- Primitive (or reference) data Type

Object

It represents instance thought witch we can access members. JavaScript object are commas.

Ex.

var person= {firstName;”Manish”,lastName:”Shukla”,age:30,eyecolor:”black”};

Array

It represents group of similar values.java script arrays are written with square brackets. 

Array items are separated by commas.

Ex.

Var student Name= [“Manish”,”Asish”,”Puneet”]                           

 

RegExp

It represents regular expression.

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