mergeSortedArrays.js

function isEmpty(array) {
  return array.length == 0;
}

function mergeSortedArrays(array1, array2) {
  result = [];

  // If there's anything in any of the arrays...
  while (!isEmpty(array1) && !isEmpty(array2)) {
    // ...we'll compare which one has the smallest next element...
    if (array1[0] < array2[0]) {
      // ...and add it to the end of result, removing it from the original array
      result.push(array1.shift());
    } else {
      result.push(array2.shift());
    }
  }

  // at the end, we simply finish inserting the rest of the elements of
  // whatever array has still elements in it. This avoids missing elements
  // when the arrays have different sizes.
  while (!isEmpty(array1)) {
    result.push(array1.shift());
  }

  while (!isEmpty(array2)) {
    result.push(array2.shift());
  }

  return result;
}