JavaScript Data Types

String, Number, Boolean, Array, Object, Null, Undefined.

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JavaScript String

A string is a variable which stores a series of characters like "John Doe".

A string can be any text inside quotes. You can use simple or double quotes:

var carname="Volvo XC60";
var carname='Volvo XC60';

You can use quotes inside a string as long as they don't match the quotes surrounding the string:

var answer="It's alright";
var answer="He is called 'Johnny'";
var answer='He is called "Johnny"';

Or you can put quotes inside a string by using the \ escape character:

var answer='It\'s alright';

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JavaScript Number

JavaScript has only one type of number.

Numbers can be with or without decimals:

var pi=3.14;
var x=34;

The maximum number of decimals is 17.

Extra large or extra small numbers can be written with scientific notation:

var y=123e5;    // 12300000
var z=123e-5;   // 0.00123

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JavaScript Boolean

Booleans can have only two values: true or false.

var x=true
var y=false

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JavaScript Array

The following code creates an Array object called myCars:

var cars=new Array();
cars[0]="Saab";
cars[1]="Volvo";
cars[2]="BMW";

or (condensed array):

var cars=new Array("Saab","Volvo","BMW");

or (literal array):

var cars=["Saab","Volvo","BMW"];

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JavaScript Object

An object is delimited by curly braces. Inside the braces the object's properties are defined as name and value pairs (name : value). The properties are separated by commas:

var person={firstname:"John", lastname:"Doe", id:5566};

The object (person) in the example above has 3 properties: fistname, lastname, and id.

Spaces and line breaks are not important:

var person={
firstname : "John",
lastname  : "Doe",
id        :  5566
};

You can address the object properties in two ways:

name=person.lastname;name=person["lastname"];

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Null or Undefined

Non-existing is the value of a variable with no value.

Variables can be emptied by setting the value to null;

cars=null;
person=null;

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Declaring Variable Types

When you declare a new variable, you can declare its type using the "new" keyword:

var carname=new String;
var x=      new Number;
var y=      new Boolean;
var cars=   new Array;
var person= new Object;

	All variables in JavaScript are objects. When you declare a variable you create a new object.