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How to flatten a given array up to the specified depth in JavaScript ?

  • Last Updated : 08 Apr, 2021
Geek Week

In this article, we will learn how to flatten a given array up to the specified depth in JavaScript.

The flat() method in JavaScript is used to flatten an array up to the required depth. It creates a new array and recursively concatenates the sub-arrays of the original array up to the given depth. The only parameter this method accepts is the optional depth parameter (by default: 1). This method can be also used for removing empty elements from the array.

Syntax:

array.flat(depth);

Example:

HTML




<html>
  <body>
    <h1 style="color: green;">
      GeeksforGeeks
    </h1>
    <b>
      How to flatten a given array up to 
      the specified depth in JavaScript?
    </b>
    <script>
  
      // Define the array
      let arr = [1, [2, [3, [4, 5], 6], 7, 8], 9, 10];
  
      console.log("Original Array:", arr);
  
      let flatArrOne = arr.flat();
  
      console.log(
        "Array flattened to depth of 1:",
        flatArrOne
      );
  
      let flatArrTwo = arr.flat(2);
  
      console.log(
        "Array flattened to depth of 2:",
        flatArrTwo
      );
  
      let flatArrThree = arr.flat(Infinity);
  
      console.log(
        "Array flattened completely:",
        flatArrThree
      );
    </script>
  </body>
</html>

Output:

Original Array: [1, [2, [3, [4, 5], 6], 7, 8], 9, 10]
Array flattened to depth of 1: [1, 2, [3, [4, 5], 6], 7, 8, 9, 10]
Array flattened to depth of 2: [1, 2, 3, [4, 5], 6, 7, 8, 9, 10]
Array flattened completely: [1, [2, [3, [4, 5], 6], 7, 8], 9, 10]

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