How to Use a JS Map in Your Coding?

How to Use a JS Map in Your Coding?
How to Use a JS Map in Your Coding?


Historically, before the introduction of JS Map, objects were used to carry out the functionalities of maps. Maps are similar to objects, as both let users assign keys to values, allowing the retrieval of those values. However, JS Map can remember the original order of insertion of the keys, removing the chances of the initial order being jumbled.

Fundamentally, using the JavaScript .map function allows the iteration of an array, allowing the modification of its elements using callback functions. Callback functions are then implemented in a loop on every element inside the array. Using JS Map while coding allows developers to work much more effectively and consume less time.

The map is a class that allows users to effectively map values, object and array classes are not especially great at this task. JS Map allows users to avoid spending extra time adding additional codes and approach operations more directly in JavaScript

What is a JS Map?

In JavaScript, a map can be defined as a class that contains elements with designated keys while their primitive value is stored. JS Map also allows users to effectively map two values. The map function creates a new array from the original elements in given arrays. JS Map uses the method to implement functions on the elements contained in the array such as multiplication, division and combinations. 

The .map function allows the iteration of an array, allowing its elements to be manipulated using callback functions. Callback functions are then implemented in a loop on every element inside the array. Fundamentally, JS Map creates the arrays by calling specific functions from all the elements the parent arrays contain.

Here are some popular properties and methods which can be used in JS Map:

  • Users can acquire iterators for the keys in a JS Map using the keys method.
  • Users can acquire iterators for the value in a JS Map using the values method.
  • The size property allows users to find out the size of the map.
  • The entries method allows users to acquire an array of the arrays with key-value pairs.
  • One can remove every key-value pair using the clear method in a JS Map.

Let us check how maps can be used with different elements and values inside JavaScript.

Using on a Javascript array,

If the array is let arr = [3, 4, 5, 6]
Then, after using the,

let arr = [3, 4, 5, 6];
let modifiedArr ={
    return element *3;

Using a map with an array of objects,If the array of objects contain the first names and surnames of people such as let

blog banner 1
users = [
  {firstName : "Susan", surname: "Steward"},
  {firstName : "Daniel", surname: "Longbottom"},
  {firstName : "Jacob", surname: "Black"}
Then, after using map method, 
let users = [
  {firstName : "Susan", surname: "Steward"},
  {firstName : "Daniel", surname: "Longbottom"},
  {firstName : "Jacob", surname: "Black"}
let userFullnames ={
    return `${element.firstName} ${element.surname}`;

// ["Susan Steward", "Daniel Longbottom", "Jacob Black"]

How to Use a JS Map?

Here is how one can use JS Map to effectively get faster results while coding.

  • Firstly, a map must be created with parameters, without which an empty map will be created, which behaves like an empty object. If users wish to fill the map with primitive values, then an iterable value like that of arrays needs to be used. Here, the inner arrays’ values which lie first are decided as keys and the second values are values for the key-value pairs.
  • Once a map is created, users need to use the .set method to insert the values there.
  • Then the user needs to use the .get method to pass the keys that need to be acquired and get the values. The user can double-check to see if the JS Map has a value stored already by using the .has method.
  • If required, the user then needs to proceed with the last Create, Read, Update and Delete or CRUD function by using the .delete method and simply removing the keys that are not required.
  • The user can then finally use .forEach to allow iteration over the map using the callback function with the key and value as parameters.

Work on Accenture Mock Test Series for off-campus placement with Coding Ninjas.

Here is an example of how the .set method can be used for storing data in the map:

let Friends= new Map()
Friends.set('Jane', {Mobile: "4321-1234", email: ""})

Advantages of using JS Maps

Here are some fundamental advantages that the Map function offers:

  • A map allows users to use objects, functions, strings, etc. as keys within the map. Unlike objects that are limited to using only strings as keys, the map can contain any value as keys. JS Map also removes the chance of including accidental keys as maps only contain keys that are specified.
  • Maps allow the keys to be accurately arranged in an order that follows when the keys were initially added; this makes it especially easy to loop. Unlike objects, maps are quite reliable when ordering the keys. Objects end up ordering keys differently due to a lack of standardisation and different iteration methods.
  • Maps support iteration natively and allow users to directly use it with methods such as ForEach. Other classes do not natively offer iteration and separate codes much be used for looping the key or value pairs inside.
  • Maps offer a size property similar to that of arrays; this allows users to find out the exact number of key or value pairs in the map. This allows users to avoid manually calculating the length. 
  • JS Map allows projects to be worked on and continued faster. Maps are optimised and built for insertion or removal of key-value pairs, hence being better when working with projects which require frequent modifications such as these. 
  • JS Map allows users to work more effectively, using more functions and much more rapidly in comparison to working with other classes or without maps.

Read about, “How does online JavaScript Compiler work?”

Examples of Utilising JS Maps

Here are some examples of using JS Map to help working with various arrays, sets of information and functions. JS Map can be used to effectively map the keys with each other and with key-value pairs for various functional, operation and mathematical tasks.

Example 1: Using JS Map for finding the square root of numbers

<p>Find the square root of each element in the array.</p>
<button onclick="myFunction()">Click here to execute</button>
<p id="demo"></p>
var integers= [9, 25, 36, 64];
function myFunction() {
  x = document.getElementById("demo")
  x.innerHTML =;

Example 2: Using JS Map to multiply numbers

<p>Every integer will be multiplied with 20:</p>
<p id="demo"></p>
var integers = [15, 22, 35, 48];
var newarray =
function myFunction(num) {
  return num * 20;
document.getElementById("demo").innerHTML = newarray;

Example 3: Using JS Map to combine elements from arrays

<p>Create a fresh array with the full name of every person in the array.</p>
<button onclick="myFunction()">Click to execute</button>
<p>New array: <span id="demo"></span></p>
var people= [
  {firstname : "Ron", lastname: "Walsh"},
  {firstname : "Alan", lastname: "Bale"},
  {firstname : "John", lastname: "Cobb"}
function getTheFullName(item) {
  var The full name = [item.firstname,item.surname].join(" ");
  return The full name;
function myFunction() {
  document.getElementById("demo").innerHTML =;

Frequently Asked Questions

What is a JS Map?

JS Map is a class that can contain elements and assign them keys while storing their pre-existing values to assist in the implementation of functions.

Is JavaScript Map a HashMap?

Yes, JS Map is a HashMap and comes native in JavaScript. HashMap is referred to by this term as it is powered by a method known as Hashing, which is a technique involving the conversion of large strings to smaller strings that fundamentally represents the same values and the same string.

What is new map JavaScript?

New Map is used when a JS Map is created and allows users to create new maps either pre-determined values or new values.

How do you map an object?

An object can be mapped using the objects.keys method and by inserting the value of the objects and then stating the object that will be mapped.

What are the parameters in the method?

There are two main parameters in the method, function and thisValue. The function parameter consists of three parameters, currentValue, Index and arr. The thisValue parameter is optional and contains the value passed for the function.

How do you group an array in JavaScript?

An array of objects can be grouped using the reduce method which executes the reducer function which is applied to the elements of the array. This results in a single value during output.

Can I map an array inside an array?

Yes, one can map an array inside an array by using maps to create a two-dimensional array where every element in the array is an array consisting of two items, the key and the value.

Are JS Maps useful?

Yes, maps can prove to be highly useful when there is a requirement of iteration or implementation of functions inside arrays using the elements inside.

Is JS Map easy to learn and use?

Yes, it can be easily learnt and is very easy to use. One can easily use maps for lookup and dictionary related tasks. Maps are incredibly easy to use with values, arrays and objects, being simple to effectively use for mapping values and keys or when functions are being stated.

Key Takeaways

Map class is supported by the latest editions of Google Chrome, Microsoft Edge, Opera, Mozilla Firefox, Safari, Internet Explorer and other browsers, including mobile browsers such as Samsung Internet and Node.Js.

Using maps makes developing in JavaScript faster, versatile and allows users to acquire the results they want with accuracy. JS Map is a very useful class that can be used instead of objects and other classes to implement various functions and tasks.

Have a doubt in mind? Get it resolved from our video or mentors!

Maps allow faster scripting and more effective use of coding, promoting lesser codes and more effectiveness by offering support for various functions and values.