In-place insert sort.

insertsort.js

const insertSort = array => {
  for(let i = 1; i < array.length; i++) {
    const el = array[i];
    let j = i - 1;

    while(j >= 0 && el < array[j]){
      array[i--] = array[j];
      array[j] = el;
      j--;
    }
  }

  return array;
}