Flatten an nested array using JavaScript

Problem statement: There is an array containing elements as an array and those array elements can contain other elements as an array and so on. Now we have to convert this input array to a flat array that contains elements but not an array of elements.

Example: Input: [1,2,3,[4,5,[6,7]],8,[9,[10,11]]] Output: [1,2,3,4,5,6,7,8,9,10,11]

Solution

function flatten(arr) {
  let flattenArr = [];
  arr.forEach(el => {
    if(Array.isArray(el)){
      const result = flatten(el);
      result.forEach(el => flattenArr.push(el));
    } else {
      flattenArr.push(el);
    }
  });
  return flattenArr;
}

const input = [1,2,3,[4,5,[6,7]],8,[9,[10,11]]];
const output = flatten(input);

console.log(output);

We have used recursion to solve this problem

Algorithm steps:

• First, we iterate through the given array.
• Then check each element:
  • if it is not an array then push the elements in an updated array.
  • if it is an array then again call the same function flatten() i.e. recursion. Then we will combine our updated array and return values of flatten() using the spread operator in ES6. This will keep flatting the updated array.

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