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# 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, ]]];`` ` `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, ]]];`` ` `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, ]]];`` ` `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:

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