Parse out the nested elements of an array into the main array

Question

What is the most efficient way to move the elements within the nested portion of the inner array out into the main array?

Example: [1,[2,3],4] -> [1,2,3,4]

my attempt

var old_arr = ["one", ["two", "three"], "four"];
var new_arr = [];

function arrayfix(arr) {
  for (var i = 0; i < arr.length; i++) {
    if (typeof arr[i] == typeof {}) { //checks to see if it's an object
      for (var j = 0; j < Object.keys(arr[i]).length; j++) {
        new_arr.push(arr[i][j]);
      }
    }
    new_arr.push(arr[i]);
  }
  return new_arr;
}

console.log(arrayfix(old_arr));

actual outcome

[ 'one', 'two', 'three', [ 'two', 'three' ], 'four' ]

desired outcome

[ 'one', 'two', 'three', 'four' ]

Answer 1

There is a built-in prototype function in Array called flat for that purpose.

One parameter: The depth level specifying how deep a nested array structure should be flattened. Defaults to 1.

flat() will flat a 2D to 1D flat(2) will flat out a 3D to 1D.

var old_arr= ["one",["two","three"],"four"];
console.log(old_arr.flat());

Answer 2

flat function is what you are looking for.

var old_arr= ["one",["two","three"],"four"];
var new_arr = old_arr.flat(); 
console.log(new_arr);

Answer 3

Either use the Array#flat() method, like Amila Senadheera suggested, or change your function to not always add the element to the new array, like so:

var old_arr= ["one",["two","three"],"four"];

function arrayfix(arr){
    let new_arr = [];
    for(let i =0; i < arr.length; i++) {
        if(typeof arr[i] == typeof {}) { //checks to see if it's an object
            for(let j =0; j < Object.keys(arr[i]).length; j++) {
                new_arr.push(arr[i][j]);
            }
        } else { // if it's an array, don't add it back to the new array
          new_arr.push(arr[i]);
        }
        
    }
    return new_arr;
}

console.log(arrayfix(old_arr));