Tutorials - JavaScript - Variables

Variables in JavaScript are usually declared (created) with the var keyword. They may be given a value at this time, or left undefined to be used later. Variables do not have to be declared before they are used - JavaScript will declare them itself the first time they are used. Variable names must start with a letter or an underscore, and can contain letters, numbers, and underscores. Remember that JavaScript is case-sensitive, so variables with different capitalization are considered different variables. Some examples:

var x;      //Declaring a variable but leaving it undefined (no value).
var y=5;    //Declaring and defining a variable in one statement.
z=10;       //Using a variable without having declared it - this is done automatically.

var 2ndVariable;            //This is not valid, as variable names cannot start with a number.

var myVariable = "Hello";   //A variable containing a string (text) value.
var myvariable = "World";   //Yes, this is a different variable, since the 'v' is lower-case!

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