JavaScript Variables

Like any other programming language, variables in JavaScript are containers for storing different types of values. A variable can be thought of as a container. We can store data into a variable and can refer the data with the help of that variable later.

Variable declaration

Before using a variable, we need to create it first. Creating a variable is called variable declaration. A variable in JavaScript can be declared by using the ‘var’ keyword.

Consider the example given below

    var x;
    var car;

You can also declare multiple variables in a single statement as follows.

    var x, car;

Rules for variable declaration

While declaring a variable, you should keep in mind that –

  1. You can not use a JavaScript reserved keyword for a variable name. For example ‘if’ and ‘else’ are two of the keywords. A list of all of the JavaScript Keywords is given in the next section below.
  2. A JavaScript Variable name cannot start with a number. It can begin either with a letter or with an underscore (_) symbol. For example 1car is an invalid variable but car1, _car are valid variable names.
  3. Variable names in JavaScript are case sensitive. For example car and CAR are two different variable names and not the same.

Reserved Keywords in JavaScript

Reserved keywords in a programming language is a set of predefined keywords that are meant for the compiler/Interpreter. JavaScript has the following set of predefined keywords-

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

Variable initialization –

Initializing a variable means storing some data or value in it. You can initialize a variable at the time of creation (declaration) or after declaration later.

For example –

    //Initialization after declaration.
    var x;
    x = 10;


    //Initialization at the time of declaration.
    var x = 10;