How to use method in JavaScript

The method was introduced in ES6 (ECMAScript 2015) for iterating and manipulating elements of an array in one go. This method creates a new array by executing the given function for each array's element.

The method accepts a callback function as a parameter you want to invoke for each item in the array. This function must return a value after performing all the modifications.

The callback accepts up to three operational parameters. The first is the current item in the iteration, the second is the index of the current item in the array, and the third is the array itself.

Let us look at the following example:

const prices = [45, 9.99, 33, 50]

const updatedPrices = => '$' + price)

// ['$45', '$9.99', '$33', '$50']

As you can see above, we used the map() function to iterate over an array of numbers and convert its elements to strings by prepending a currency symbol. The updatedPrices variable is a newly created array with the results of executing a function for each item in the parent array.

Keep in mind that the is a non-mutating function, which means that it doesn't change the original array and only relies on the results of the provided function to create a new array.

The range of elements processed by the map() function is decided before the first invocation. If new items are added to the array after the map() begins, they won't be processed by the callback.


In addition to iterating over all elements of an array and transforming them, the map() method can be used to do more things. Let us look at a few more examples below.

Extracting values from an array of objects

The map() method is extremely useful to extract values from an array of objects. Let us say you have the following JSON array that contains users' names and their ages:

const users = [
        name: 'John Deo',
        age: 35
        name: 'Emma Kel',
        age: 24
        name: 'Kristy Adam',
        age: 42

Here is an example that uses map() to extract all ages and returns them as a new array:

const ages = => user.age)

// [35, 24, 42]

Transforming an array of objects

The map() method can be used to iterate over all objects in an array, transform the content of each individual object, and return a new array. Here is an example:

const modifiedUsers = => {
  // assign a random color to each user
  user.color = '#' + ((Math.random() * 0xffffff) << 0).toString(16)

  // return modified user
  return user


// [
//   { name: 'John Deo', age: 35, color: '#f76f4b' },
//   { name: 'Emma Kel', age: 24, color: '#e05341' },
//   { name: 'Kristy Adam', age: 42, color: '#48242c' }
// ]


The method in JavaScript is used to iterate over all array elements and creates a new array. Here are a few things that you should remember about

  1. It calls the provided function for each element in an array and returns a new array.
  2. It doesn't modify the original array contents and only creates a new array with the values returned by the invoked function.
  3. New elements added to the array after the map() function begins are not processed.

The method works in all modern browsers and Internet Explorer 9 and above. You can use a polyfill to support IE6 and higher.

Read this article to learn more about JavaScript arrays and their methods.

✌️ Like this article? Follow me on Twitter and LinkedIn. You can also subscribe to RSS Feed.

You might also like...

Digital Ocean

The simplest cloud platform for developers & teams. Start with a $200 free credit.

Buy me a coffee ☕

If you enjoy reading my articles and want to help me out paying bills, please consider buying me a coffee ($5) or two ($10). I will be highly grateful to you ✌️

Enter the number of coffees below:

✨ Learn to build modern web applications using JavaScript and Spring Boot

I started this blog as a place to share everything I have learned in the last decade. I write about modern JavaScript, Node.js, Spring Boot, core Java, RESTful APIs, and all things web development.

The newsletter is sent every week and includes early access to clear, concise, and easy-to-follow tutorials, and other stuff I think you'd enjoy! No spam ever, unsubscribe at any time.