How to flatten a nested array in JS | Recursion | Javascript Interview | 1

How to flatten a nested array in JS | Javascript Interview

Array = [1,2,[3,4,[5,6],7],8,[9,[10,11]]]  

Required output: [1,2,3,4,5,6,7,8,9,10,11] 

We are going to write a recursive function i.e the function which calls itself to flatten a nested array

• We are going to loop through the array and check if the item is an array
• If it is, we are going to loop through that item by passing that to the function 
• If it is not then we will push it to another array(blank initially)

Let's look at the code:

function Flat(myArray, newArray=[]){
 for(let i = 0; i < myArray.length; i++) { 
  if(Array.isArray(myArray[i])){ 
  // We are using isArray method of Array Prototype
   Flat(myArray[i],newArray)  // call the function again with the current array in myArray[i];
  } 
  else {  
   newArray.push(myArray[i]) 
   // if myArray[i] isn't a array, push it to new array
  } 
 }
 return newArray
}

Now, this solution is intended for people with less than 1 YOE in Javascript. If you have better understanding of Javascript, you can go ahead with the below solution in order to flatten a nested array in Javascript:

function flat(myArray, newArray=[])
{
 myArray.forEach((item) => (Array.isArray(item))?flat(item, newArray)
 :newArray.push(item))
 return newArray
}

There are several ways to flat an array in Javascript, please share your solutions in comment section. With increasing experience, you will be asked different variations of this concept. 

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