Array splice implementation to convert an existing array to target array

array_splice.js

(() => {
  /**
 * Fill gaps of an array
 * @param {Object} sourceArray - The source array to compare to
 * @param {Object} targetArray - The target array to fill the gap
 * @param {string} Filler - The element to be used to fill the gap
 */
  let similarFill = ((sourceArray, targetArray, filler) => {
    let pos = 0;
    for (let i = 0; i < targetArray.length; i++) {
      // if position is greater or equal of the source array length, then set position as 0
      if (pos >= sourceArray.length) {
        pos = 0;
      }
      // if target element is not same as source element, then insert the filler element at that point
      if (targetArray[i] != sourceArray[pos]) {
        targetArray.splice(i, 0, filler);
      }
      // increase position along with the loop
      pos += 1;
    }
    return targetArray;
  })

  // Example Usage
  let sourceElem = [1, 2, 3, 4, 5, 6];
  let targetElem = [
    1, 2, 3, 4, 5, 6,
    1, 2, 3, 4, 5, 6,
    2, 3, 4, 5, 6,
    1, 3, 4, 5, 6,
    1, 4, 5, 6
  ];

  let resultElem = [
    1, 2, 3, 4, 5, 6,
    1, 2, 3, 4, 5, 6,
    0, 2, 3, 4, 5, 6,
    1, 0, 3, 4, 5, 6,
    1, 0, 0, 4, 5, 6
  ];

  // verify our function
  // check if array is identical https://stackoverflow.com/a/4025958
  function arraysEqual(arr1, arr2) {
    if (arr1.length !== arr2.length)
      return false;
    for (var i = arr1.length; i--;) {
      if (arr1[i] !== arr2[i])
        return false;
    }
    return true;
  }
  console.log(arraysEqual(similarFill(sourceElem, targetElem, 0), resultElem))
})()