merge_two_sorted_arrays.js

const arr1 = [1, 7, 13, 15];
const arr2 = [1, 4, 5, 9, 20];

const merge = (arr1, arr2) => {
  let merged  = [];
  let index1  = 0;
  let index2  = 0;
  let current = 0;
  
  while(current < (arr1.length + arr2.length)) {
    let i = arr1[index1];
    let j = arr2[index2];
    
    if(i < j) {
      merged[current] = i;
      index1++
    } else {
      merged[current] = j;
      index2++;
    }
    
    current++
  }
  
  return merged; // should be return [1, 1, 4, 5, 7, 9, 13, 15, 20]
}