Difference between revisions of "Introducing JavaScript Variables"

Revision as of 18:24, 11 April 2007

Variables are a key element of just about every programming language ever invented, and just like other programming langauges, an understanding of the basics of JavaScript variables is key to learning this scripting langauge.

Variables are nothing more than a way to store information in memory. A variable can be a number, a single character, a string of characters making up a work or sentence, or a value indicating whether something is true or false. In JavaScript you declare a variable by giving it a name and assigning a value to it. You can then access this data at any time and, more importantly, change either the content of the variable whenever necessary (hence the name variable).

Variables are assigned and manipulated using operators which will be covered in a later chapter. At this stage it is important to understand one operator in particular - the assignment operator.

Variable Declaration and the Assignment Operator

Varaibles in javaScript are declared by by specifying the name name of the variable storage you wish to create prefixed with the token var. For example, to create a variable named myVariable:

var myVariable;

The above line creates a new variable which can be accessed using the name myVariable but does not assign any initial value.

Note that whilst it is also possible to declare a variable without the var token this is strongly discouraged. Failing to specify the 'var' before the variable can cause confusion when variables with the same name are present in local and global scopes. Good practice dictates that all variable declarations be prefixed with the var token.

The '=' assignment operator can subsequently be used to assign a new value to our variable:

myVariable = 10;

In this instance the variable which had already declared is asssigned the to contain an integer value of 10.