Array Flatten in JavaScript

Array can store all data types of value like, String, number, boolean, object and Array too. yes Arary can store another array in the single value in it. so,

If Array has values of another Arrays so we call it Nested Arrays

let numbers = [1, 2, [3, 4], [5, 6]];

• Main array contains normal values

• It also contains smaller arrays inside it

Nested arrays are common in:

• API responses

• Menu structures

• Categories/subcategories

• Matrix data

• Tree-like structures

Sometimes we need all values in one simple array.

[1, [2, 3], [4, 5]] // nested arrays
[1, 2, 3, 4, 5] // flatten arrays

Flatten Arrays

Flattening converts a nested structure into a single flat list

Approches to convert nested to flatten arrays

1) Using .flat() (modern js)

let arr = [1, 2, [3, 4], [5, 6]]; //nested array 
let result = arr.flat(); // flatten and store on another var
console.log(result); //[1, 2, 3, 4, 5, 6]

.flat() Flatten all levels of arrays

2) Using Loops

let arr = [1, 2, [3, 4]];
let result = [];

for (let i = 0; i < arr.length; i++) {
  if (Array.isArray(arr[i])) {
    result = result.concat(arr[i]);
  } else {
    result.push(arr[i]);
  }
}

console.log(result);

When flattening arrays:

• Check each item

• If normal value → add directly

• If array → take values out

• Repeat until fully flat

3) Using Recursion

function flatten(arr) {
  let result = [];

  for (let item of arr) {
    if (Array.isArray(item)) {
      result = result.concat(flatten(item));
    } else {
      result.push(item);
    }
  }

  return result;
}

console.log(flatten([1, [2, [3, 4]]]));

Method	Best For
flat()	Simple and modern
Loop + concat	Beginner understanding
Recursion	Interviews and deep nesting

Summary

Nested arrays = arrays inside arrays
Flattening = converting into one simple array
Use .flat() for easy cases
Learn recursion
Always think step-by-step while solving

Array Basics