What are the JavaScript data types

JavaScript data types

JavaScript variables can hold different data types: numbers, strings, objects and more:
let length = 16;                                                                           // Number

let lastName = “shubh”;                                                            // String

let x = {firstName:”shubh, lastName:”laxakar”};                   // Object

The Concept of Data Types

In programming, data types is an important concept.To be able to operate on variables, it is important to know something about the type.Without data types, a computer cannot safely solve this:

let x = 16 + “xuv700”;

Result: 16xuv700
Does it make any sense to add “Volvo” to sixteen? Will it produce an error or will it produce a result?

JavaScript will treat the example above as:

let x = “16” + “xuv700”;

When adding a number and a string, JavaScript will treat the number as a string.
JavaScript evaluates expressions from left to right. Different sequences can produce different results:

let x = 16 + 4 + “xuv700”;

Result: 20xuv700

let x = “Volvo” + 16 + 4;

JavaScript Types are Dynamic

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


let x;                            // Now x is undefined

x = 5;                           // Now x is a Number x = “John”;     // Now x is a String

JavaScript Strings

A string (or a text string) is a series of characters like “John Doe”. Strings are written with quotes. You can use single or double quotes:

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


let answer1 = “It’s alright”;                       // Single quote inside double quotes

let answer2 = “He is called ‘Johnny'”; // Single quotes inside double quotes

let answer3 = ‘He is called “Johnny”‘; // Double quotes inside single quotes

JavaScript Numbers

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


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

JavaScript Booleans

Booleans can only have two values: true or false.


let x = 5; let y = 5; let z = 6;

(x == y)    // Returns true

(x == z)    // Returns false

JavaScript Arrays

JavaScript arrays are written with square brackets. Array items are separated by commas.

The following code declares (creates) an array called cars, containing three items (car names):


const cars = [“Saab”, “Volvo”, “BMW”];

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

JavaScript Objects

JavaScript objects are written with curly braces {}.

Object properties are written as name:value pairs, separated by commas.


const person = {firstName:”John”, lastName:”Doe”, age:50, eyeColor:”blue”};

The typeof Operator

You can use the JavaScript typeof operator to find the type of a JavaScript variable. The typeof operator returns the type of a variable or an expression:


typeof “”                                // Returns “string”

typeof “John”                         // Returns “string” typeof “John Doe”                                              // Returns “string”

typeof 0                                 // Returns “number”

typeof 314                             // Returns “number”

typeof 3.14                            // Returns “number”

typeof (3)                               // Returns “number” typeof (3 + 4)                                              // Returns “number”


In JavaScript, a variable without a value, has the value undefined. The type is also undefined.


let car;              // Value is undefined, type is undefined

car = undefined;                // Value is undefined, type is undefined

Empty Values

An empty value has nothing to do with undefined. An empty string has both a legal value and a type.


let car = “”;      // The value is “”, the typeof is “string

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Detailed Example of Datatype

<h2>JavaScript Variables</h2>
<p>In this example, x, y, and z are variables.</p>
<p id=”demo”></p>
let x = 5;
let y = “shubh”;
let z=””;
const person = {firstName:”John”, lastName:”Doe”, age:50, eyeColor:”blue”};
const cars = [“xuv700”, “Volvo”, “BMW”];
document.write(“Car Name=” +cars[0]);
document.write(“<br>Car Name=” +cars[1]);
document.write(“<br>Car Name=” +cars[2])
document.write(“<br> Type of x=”+typeof(x))
document.write(“<br> Type of y=”+typeof(y))
document.write(“<br> Type of Person=”+typeof(person))
document.write(“<br> Type of Cars=”+typeof(cars))
document.write(“<br> Type of z=”+typeof(z))


What are the JavaScript data types

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