Lodash _.flattenDeep() and _.flattenDepth() Method

Lodash _.flattenDeep() Method

The _.flattenDeep() method is used to completely flatten nested arrays. It does this recursively.

Syntax:

_.flattenDeep( array )

Parameters: This method accepts single parameter as mentioned above and described below:

• array: This parameter holds the array that to be flatten.

Return Value: This method returns the new flattened array.

Example:

const _ = require('lodash');

let ar = [1, [2, [3, 4, [5]]]];

let flattenArray = _.flattenDeep(ar);

console.log(flattenArray);

Here, const _ = require('lodash') is used to import the lodash library into the file.

Output:

[ 1, 2, 3, 4, 5 ]

Lodash _.flattenDepth() Method

The _.flattenDepth() method is used to flatten up to depth time that is passed into the function.

Syntax:

_.flattenDepth(array, depth)

Parameters: This method accepts two parameters as mentioned above and described below:

• array: This parameter holds the array that need to be flatten.
• depth: This parameter holds the maximum recursion depth.

Return Value: This method returns the new flattened array.

Example 1: Flatten to depth 1

const _ = require('lodash');

let ar = [1, [2, [3, 4, [5]]]];

let flattenArray = _.flattenDepth(ar, 1);

console.log(flattenArray);

Output:

[ 1, 2, [ 3, 4, [ 5 ] ] ]

Example 2: Flatten to depth 2

const _ = require('lodash');

let ar = [1, [2, [3, 4, [5]]]];

let flattenArray = _.flattenDepth(ar, 2);

console.log(flattenArray);

Output:

[ 1, 2, 3, 4, [ 5 ] ]

Note: This will not work in normal JavaScript because it requires the library lodash to be installed.

Reference:

• https://lodash.com/docs/4.17.15#flattenDeep
• https://lodash.com/docs/4.17.15#flattenDepth