JavaScript Data Types and Data Structures

By | October 29, 2021
JavaScript Data Types and Data Structures

Every Programming Language has its built-in data types and data structures. Although most of the Programming Languages share the same concepts for Data Types and Data Structure, there are some which support unique Data Types and Data Structure.

Here in this JavaScript tutorial, you will learn all the built-in Data Types and Structures present in JavaScript.


Data Types in JavaScript

When we declare or initialize a variable in JavaScript, we do not define its data type because JavaScript is a Dynamically types programming language. If you have ever worked with static-typed programming languages like C++, C and Java there we need to define the variable datatype when we declare a variable.

In Static-Typed C++ Language

int age =  23;

In Dynamic-Typed JavaScritp Language

age = 23;

In the above code snippet, you can see that in C++ we defined int (integer) data type to the age variable but in JavaScript, we did not need to define the variable type, because JavaScript is a Dynamic-Typed language, and the JavaScript engine handles the type specification for us.

So what is a Data Type?

A Data Type defines the type of value that a variable is holding. For example, if a variable is holding a number value then its Data type will be number in JavaScript, if it is holding a text value then its type will be the string.

Types of Data Types in JavaScript

According to the Latest ECMAScript Standard, the JavaScript Data Types are divided into 2 categories.

  1. JavaScript Primitive Data Types
  2. JavaScript Non-Primitive or Structural Data Types.

JavaScript Primitive Data Types

There are 7 built-in Primitive Data Types present in JavaScript

  1. Number
  2. String
  3. Boolean
  4. undefined
  5. Null
  6. Bigint (New)
  7. Symbol (New)

1. Number 

If a variable is holding a decimal or non-decimal number value such as integer, real-number, whole number, or natural number, then the data type of the variable would be number.


let num1 = 1223;
let num2 = 122.2323;
let num3 = -2323.33;
let num4 = 0;

2. String

A string is a text value that can be contained inside the pair of single quotes ‘ string' , double quotes "string"  or backticks `string`.


//with single quote
let string1 = 'one*()101'

// with double quote
let string2 = "two 222@@"

//with backticks
let string3 = `three 3333@@@`

3. Boolean

The Boolean data type defines true and false in JavaScript, and it has only two value true and false.


let adult = true;
let adult = false;

4. Undefined

The undefined is not a value it is a state or data type assigned to a variable when it is only declared not initialized.


//here a is undefined
let a;

5. Null

The null is a special data type value, and it is used when you want to assign no value to the variable rather than leaving it undefined.

The data type of null value is objectwhich is a structural Data type.

// null value
let email = null

6. Bigint

Bigint stands for big integer and is the new data type introduced to JavaScript in the latest ECMAScript standards. By default the maximum number the JavaScript can deal with is 253which is 9007199254740992but if we wish to use a number greater than 253 then we can use the Bigint data type in JavaScript.

To initialize a Bigint number in JavaScript we can either use the Bigint() object or place n at the end of the number.


let bignum = BigInt(23); 

// put n at last 
let bignum2 = 23n;

7. Symbol

Symbol is also a new data type introduced to JavaScript in the latest ECMASccript standards. To define a Symbol data type in JavaScipt we can use Symbol() object.

The Symbol data type is used to create unique and immutable values, two symbols data type values can not be equal.


let sym1 = Symbol(1); 
let sym2 = Symbol("two");

JavaScript Non-Primitive Data Types or Data Structure

There are two major and widely used Non-Primitive Data Types, which are also known as JavaScript built-in Data Structure.

  1. Objects
  2. Arrays

As the Name Suggest the Data Structure is used to structure the data value, and it generally structures the primitive data value or data types.

1. Objects

An object in JavaScript is a collection of name:value pairs, where the name could be a variable name and the value is the data value.

All the name:value pairs in the JavaScript object can be defined inside the curly brackets {} separated by commas.


let obj1= {name:"Rahul", age:21}

let obj2 = {name:"Ravi", age:23}

2. Array

An array in JavaScript is a sequential collection of data values. To declare an array in JavaScript we use the square brackets.

let arr = [1, 'one', 2.0, true]

How to Get the Data Type of Variable in JavaScript?

JavaScript provides a built-in typeofkeyword which returns the data type of the variable. We can use typeof operator and get the data type of the variable.


<!DOCTYPE html>
            document.write("<h1> JavaScript Data Types</h1>");

            //primitive data types
            let num = 23;
            let str = "Hello23"
            let boolean = true;
            let undef;
            let noval = null;
            let bignum = 23n;
            let symbol = Symbol("1");

            //non-primitive data types
            let obj ={name:"value1", name2:"value2"};
            let arr = [1, 2, 3,4];

            document.write('The Data Type of num is: '+typeof num);

            document.write('The Data Type of str is: '+typeof str);

            document.write('The Data Type of boolean is: '+typeof boolean);

            document.write('The Data Type of undef is: '+typeof undef);

            document.write('The Data Type of noval is: '+typeof noval);

            document.write('The Data Type of bignum is: '+typeof bignum);

            document.write('The Data Type of symbol is: '+typeof symbol);

            document.write('The Data Type of obj is: '+typeof obj);

            document.write('The Data Type of arr is: '+typeof arr);


  • Data Type defines the type of the data value.
  • JavaScript Data Types is divided into two categories primitive and non-primitive data types.
  • There are 7 primitive data types in JavaScript number, string, undefined, null, boolean, Symbol, and Bigint.
  • The non-primitive data types are also known as the Data Structure or JavaScript structural data types.
  • There are two major structural data types in JavaScript objects and Arrays.
  • To find the data type of a variable we can use the typeof operator.

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