SOURCE

let array = [7, 1, 2, 9, 8, 4];

function insert(array) {
  let arr = [];
  arr.push(array[0]);

  for (let i = 1; i < array.length; i++) {
    let inserted = false;

    for (let j = arr.length - 1; j >= 0; j--) {
      if (array[i] >= arr[j]) {
        arr.splice(j + 1, 0, array[i]);
        inserted = true;
        break;
      }
    }

    if (!inserted) {
      arr.splice(0, 0, array[i]);
    }
  }

  return arr;
}

console.log(insert(array));