JavaScript Array flatMap() Method

The Javascript array flatMap() is an inbuilt method in JavaScript that is used to flatten the input array element into a new array. This method first of all maps every element with the help of a mapping function, then flattens the input array element into a new array.

Syntax:

let A = array.flatMap(function callback(current_value, index, Array)) {
// It returns the new array's elements.
}

Parameters:

• current_value: It is the input array element.
• index:
  • It is optional.
  • It is the index of the input element.
• Array:
  • It is optional.
  • It is used when an array map is called.

Return Values: It returns a new array whose elements are the return value of the callback function.

Example 1: in this example, we will see the basic use of the array.flatMap() method for flattening an array. 

javascript

// Taking input as an array A having some elements.
let A = [1, 2, 3, 4, 5];

// Mapping with map method.
b = A.map(x => [x * 3]);
console.log(b);

// Mapping and flatting with flatMap() method.
c = A.flatMap(x => [x * 3]);
console.log(c);

// Mapping and flatting with flatMap() method.
d = A.flatMap(x => [[x * 3]]);
console.log(d);

Output

[ [ 3 ], [ 6 ], [ 9 ], [ 12 ], [ 15 ] ]
[ 3, 6, 9, 12, 15 ]
[ [ 3 ], [ 6 ], [ 9 ], [ 12 ], [ 15 ] ]

Example 2: This flatting can also be done with the help of reducing and concat.

javascript

// Taking input as an array A having some elements.
let A = [1, 2, 3, 4, 5];
console.log(A.flatMap(x => [x * 3]))

// is equivalent to
b = A.reduce((acc, x) => acc.concat([x * 3]), []);
console.log(b);

Output

[ 3, 6, 9, 12, 15 ]
[ 3, 6, 9, 12, 15 ]

We have a complete list of Javascript Array methods, to check those please go through this Javascript Array Complete reference article.

Supported Browser:

• Google Chrome 69 and above
• Edge 79 and above
• Firefox 62 and above
• Opera 56 and above
• Safari 12 and above

Note: This method is available in Firefox Nighty only.

We have a Cheat Sheet on Javascript where we covered all the important topics of Javascript to check those please go through Javascript Cheat Sheet-A Basic guide to JavaScript.