Variable means anything that can vary. JavaScript includes variables which hold the data value and it can be changed anytime.
JavaScript uses reserved keyword var to declare a variable. A variable must have a unique name. You can assign a value to a variable using equal to (=) operator when you declare it or before using it.
Syntax:
var <variable-name>;
var <variable-name> = <value>;
Example: Variable declaration & initialization
var one = 1; // variable stores numeric value
var two = 'two'; // variable stores string value
var three; // declared a variable without assigning a value
In the above example, we have declared three variables using var keyword: one, two and three. We have assigned values to variables one and two at the same time when we declared it, whereas variable three is declared but does not hold any value yet, so it's value will be 'undefined'.
Declare variables in single line:
Multiple variables can also be declared in a single line separated by comma.
Example: Multiple variables in single line
var one = 1, two = 'two', three;
Declare variable without var keyword:
JavaScript allows variable declaration without var keyword. You must assign a value when you declare a variable without var keyword.
Example: Variable without var keyword
one = 1;
two = 'two';
It is Not Recommended to declare a variable without var keyword. It can accidently overwrite an existing global variable.
Scope of the variables declared without var keyword become global irrespective of where it is declared. Global variables can be accessed from anywhere in the web page. Visit Scope for more information.
White space and line breaks:
JavaScript allows multiple white spaces and line breaks when you declare a variable with varkeyword.
Example: Whitespace and line breaks
var
one
=
1,
two
=
"two"
Please note that semicolon is optional.
Loosely-typed variables:
C# or Java has strongly typed variables. It means variable must be declared with a particular data type, which tells what type of data the variable will hold.
JavaScript variables are loosely-typed which means it does not require a data type to be declared. You can assign any type of literal values to a variable e.g. string, integer, float, boolean etc..
Example: Loosely Typed variables
var one =1; // numeric value
one = 'one'; // string value
one= 1.1; // decimal value
one = true; // Boolean value
one = null; // null value
Points to Remember :
- Variable stores a single data value that can be changed later.
- Variables can be defined using var keyword. Variables defined without varkeyword become global variables.
- Variables must be initialized before using.
- Multiple variables can be defined in a single line. e.g. var one = 1, two = 2, three = "three";
- Variables in JavaScript are loosely-typed variables. It can store value of any data type through out it's life time.