What is Array.flatMap() in JavaScript?

Array.flatMap() is a method introduced in ECMAScript 2019 (ES10) that combines the functionalities of map() and flat() methods. It first maps each element of an array using a mapping function, then flattens the result into a new array. This method is particularly useful when you want to apply a transformation to each element of an array and flatten the resulting arrays into a single array.

Syntax:

array.flatMap(callbackFn[, thisArg])

Parameters:

• callbackFn: A function that accepts up to three arguments: the current element being processed, the index of the current element, and the array being mapped.
• thisArg (optional): An object to which this a keyword can refer to inside the callbackFn.

Example: Here, the flatMap() method is called on the arr array with a callback function that doubles each element of the array and creates a new array containing both the original element and its doubled value.

Javascript

const arr = [1, 2, 3];

const result = arr.flatMap(x => [x, x * 2]);

console.log(result);

Output

[ 1, 2, 2, 4, 3, 6 ]