Value types: String, Number, Boolean, Null, Undefined, Symbol.

Reference data types: Object, Array, Function.

Note: Symbol is a new primitive data type introduced in ES6 that represents unique values.

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

The instance

var x; / / x is undefined

var x = 5; // Now x is a number

var x = “John”; // now x is a string

JavaScript string

Strings are variables that store characters such as “Bill Gates”.

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

The instance

var carname=”Volvo XC60″;

var carname=’Volvo XC60′;

You can use quotation marks in strings as long as they do not match the quotation marks surrounding the string:

The instance

var answer=”It’s alright”;

var answer=”He is called ‘Johnny'”;

var answer=’He is called “Johnny”‘;

JavaScript digital

JavaScript has only one numeric type. Numbers may be numbered with or without a decimal point:

Instance var x1 = 34.00; // Use a decimal point

var x2=34; // Do not use the decimal point to write

The greatest or smallest numbers can be written by scientific (exponential) notation:

The instance

var y=123e5; / / 12300000

var z=123e-5; / / 0.00123

JavaScript Boolean

Boolean (logic) can have only 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 later in this tutorial.

JavaScript array

The following code creates an array named 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) :

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

JavaScript object

Objects are separated by curly braces. Inside parentheses, the attributes of the object are defined as name and value pairs. Properties are separated by commas:

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

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

Spaces and folds don’t matter. Statements can span multiple lines:

var person={

 firstname : "John",

 lastname  : "Doe",
 id        :  5566
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};

Object attributes can be addressed in two ways:

Undefined and Null

Undefined Indicates that the variable has no value.

You can empty a variable by setting its value to NULL.

The instance

cars=null;

person=null;

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;

Lamp JavaScript variables are all objects. When you declare a variable, you create a new object.