Introduction to JavaScript Variables

Variables store data values. Each variable has a name, called an identifier. A variable's name is used to identify it's stored value.

Naming Variables

Identifiers must start with a letter and may contain:

• Letters
• Numbers
• Underscores
• Dollarsigns

They are case sensitive, so "myVariable" would point to a different value than "myvariable". JavaScript keywords can not be used as variable names.

Data Types

Each variable has a data type. This refers to the type of data the variable stores. Here is a list of JavaScript datatypes:

String

A string variable stores characters. The value is placed in quotation marks. See the example below.

var myStringvariable = "Hi, I am a string!";

var username = "cylon6";

Number

Number variables can store whole nubers or decimals.

var salesTax = .06;

var count = 36;

Boolean

Boolean variables have 2 possible values: true or false.

permission1 = true;

permission2 = false;

Reviewing propositional logic will help you understand boolean variables.

Array

An array stores a set of data. You will find more information on arrays in JavaScript Datasets

var games = ["Dungeons & Dragons", "Spades", "Twister"];

var grades = [96, 88, 75, 63, 58];

Object

An Object also stores sets of data. This data includes variables called properties and functions called methods. Learn more about objects in JavaScript Datasets and Objects and Constructors.

var user = {username: "cylon6", password:"jsakhd&8hj*hHG5", email: "byyourcommand@basestar.com"};

Null

A null variable does not yet have a value. You can declare a variable as null then later give it a value.

var average = null;

Undefined

An undefined variable has a value that is unkown or does not exist. If you reference a variable that isn't initalize or an object property that does not exist you will get "undefined". If you reference a variable before it has been assigned a value you will also get "undefined".

Loose Typing

JavaScript is a loosely typed language. When you declare a JavaScript variable, you do not have to specify its data type. A JavaScript variable receives its type from the value you store inside it. So a variable's type can change during the execution of a JavaScript application.