JavaScript provides different data types to hold different types of values. There are two types of data types in JavaScript.

Primitive data type
Non-primitive (reference) data type

JavaScript is a dynamic type language, means you don't need to specify type of the variable because it is dynamically used by JavaScript engine. You need to use var here to specify the data type. It can hold any type of values such as numbers, strings etc. For example:

var a=40; holding number
var b="Hamza"; holding string

JavaScript primitive data types

There are five types of primitive data types in JavaScript. They are as follows:

Data Type	Description
String	represents sequence of characters e.g. "hello"
Number	represents numeric values e.g. 100
Boolean	represents boolean value either false or true
Undefined	represents undefined value
Null	represents null i.e. no value at all

JavaScript non-primitive data types

The non-primitive data types are as follows:

Data Type	Description
Object	represents instance through which we can access members
Array	represents group of similar values
RegExp	represents regular expression

Example:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>JavaScript</title>
    <script>
        /* String Data Type */
        var a = "Hello World";
        document.write(a);
        document.write("<br>");
        document.write(typeof a);
		document.write("<br><br>");

        /* Number Data Type */
        var b = 25;
        document.write(b);
        document.write("<br>");
        document.write(typeof b);
		document.write("<br><br>");

        /* Boolean Data Type */
        var c = true;
        document.write(c);
        document.write("<br>");
        document.write(typeof c);
		document.write("<br><br>");

        /* Array Data Type */
        var d= ["HTML","CSS","JS"];
        document.write(d);
        document.write("<br>");
        document.write(typeof d);
		document.write("<br><br>");

        /* Object Data Type */
        var x= {first:"Jane",last:"Doe"};
        document.write(x);
        document.write("<br>");
        document.write(typeof x);
		document.write("<br><br>");

        /* Null Data Type */
        var y = null;
        document.write(y);
        document.write("<br>");
        document.write(typeof y);
		document.write("<br><br>");

        /* undefined Data Type */
        var z;
        document.write(z);
        document.write("<br>");
        document.write(typeof z);
		document.write("<br><br>");
    </script>
</head>
<body>
</body>
</html>