MergeSortArray.js

function mergeSortedArrays(array1, array2){
  const mergedArray = [];
  let array1Item = array1[0];
  let array2Item = array2[0];
  let i = 1;
  let j = 1;
  
  //We should actually move these 2 if statements to line 2 so that we do the checks before we do assignments in line 3 and 4!
  if(array1.length === 0) {
    return array2;
  }
  if(array2.length === 0) {
    return array1;
  }

  while (array1Item || array2Item){
   if(array2Item === undefined || array1Item < array2Item){
     mergedArray.push(array1Item);
     array1Item = array1[i];
     i++;
   }   
   else {
     mergedArray.push(array2Item);
     array2Item = array2[j];
     j++;
   }
  }
  return mergedArray;
}

mergeSortedArrays([0,3,4,31], [3,4,6,30]);