JavaScript Data types

String, number, Boolean, array, object, Null, Undefined

JavaScript has a dynamic type

JavaScript has a dynamic type. This means that the same variables can be used for different types:

Example

var x//X is Undefinedvar x = 6;      X is the number var x = "Bill"; X is a string

JavaScript String

A string is a variable that stores characters, such as Bill Gates.

The string can be any text in quotation marks. You can use single or double quotation marks:

Example

var carname= "Bill Gates"; var carname= ' Bill Gates ';

You can use quotation marks in a string, as long as you do not match the quotes enclosing the string:

Example

var answer= "Nice to meet you!"; var answer= "He is called ' Bill '", var answer= ' He is called "Bill";

JavaScript Numbers

JavaScript has only one numeric type. Numbers can be with decimal points or without:

Example

var x1=34.00;         Use the decimal point to write Var x2=34; Do not use the decimal point to write

Large or small numbers can be written by means of scientific (exponential) notation:

Example

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

JavaScript Boolean

Boolean (logic) can have only two values: TRUE or FALSE.

var X=truevar y=false

JavaScript Arrays

The following code creates an array named cars:

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

or (condensed array):

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

or (literal array):

Example

var cars=["Audi", "BMW", "Volvo";

The array subscript is zero based, so the first item is [0], the second one is [1], and so on.

JavaScript Objects

Objects are separated by curly braces. Inside the parentheses, the properties of the object are defined in the form of name and value pairs (name:value). Attributes are separated by commas:

var person={firstname: "Bill", LastName: "Gates", id:5566};

The object (person) in the example above has three attributes: FirstName, LastName, and ID.

Spaces and lines do not matter. Declarations can span multiple lines:

var person={firstname: "Bill", LastName: "Gates", id:5566};

Object properties are addressed in two ways:

Example

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

Undefined and Null

Undefined This value indicates that the variable does not contain a value.

You can empty a variable by setting the value of the variable to null.

Example

Cars=null;person=null;

declaring variable types

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

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

JavaScript variables are objects. When you declare a variable, a new object is created.

JavaScript Data types