JavaScript Data Types

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

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JavaScript Has Dynamic Types

JavaScript has dynamic types. This means that the same variable can be used as different types:

Example

var x;               // Now x is undefined
var x = 5;           // Now x is a Number
var x = "John";      // Now x is a String

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JavaScript Strings

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 single or double quotes:

Example

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:

Example

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

You will learn a lot more about strings in the advanced section of this tutorial.

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JavaScript Numbers

JavaScript has only one type of numbers. Numbers can be written with, or without decimals:

Example

var x1=34.00;      // Written with decimals
var x2=34;         // Written without decimals

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

Example

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

You will learn a lot more about numbers in the advanced section of this tutorial.

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JavaScript Booleans

Booleans can only have two values: true or false.

var x=true;
var y=false;

Booleans are often used in conditional testing. You will learn more about conditional testing in a later chapter of this tutorial.

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JavaScript Arrays

The following code creates an Array called cars:

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):

Example

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

Array indexes are zero-based, which means the first item is [0], second is [1], and so on.

You will learn a lot more about arrays in later chapters of this tutorial.

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JavaScript Objects

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: firstname, lastname, and id.

Spaces and line breaks are not important. Your declaration can span multiple lines:

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

You can address the object properties in two ways:

Example

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

You will learn a lot more about objects in later chapters of this tutorial.

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Undefined and Null

Undefined is the value of a variable with no value.

Variables can be emptied by setting the value to null;

Example

cars=null;
person=null;

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Declaring Variables as Objects

When a variable is declared with the keyword "new", the variable is declared as an object:

var name = new String;
var x =    new Number;
var y =    new Boolean;

	With JavaScript all variables can be objects.