A buggy impl of Array.prototype.filterSpliceSort

filter_splice_sort.js

Array.prototype.filterSpliceSort = function(callbackFn) {
  const returnArray = [];
  for (let index = 0; index < this.length; index += 1) {
    const value = this[index];

    const result = callbackFn(value, index, this);
    // -- Return true to keep the element
    if (true === result) {
      // nothing to see here, move along
      continue;
    }

    // -- Return false to remove it and put the element in the return array
    if (false === result) {
      // splice mutates in place, so we have now removed it
      const [splicedOutValue] = this.splice(index, 1);
      returnArray.push(splicedOutValue);
      index -= 1;
      continue;
    }

    // -- Return undefined to just remove it
    if (undefined === result) {
      this.splice(index, 1);
      index -= 1;
      continue;
    }

    // -- Any other return value puts the element into its sorted position

    // sounds like time for a super great nested loop
    const copy = [...returnArray].concat(value);

    // mmmm, mutates in place deliciousness
    copy.sort();
    const newIndex = copy.findIndex(maybeValue => maybeValue === value);

    // remove it...
    returnArray.splice(newIndex, 0, value);
  };

  return returnArray;
};

const testData = [
  1,
  2,
  'quack',
  3,
  null,
  4,
  5,
  {},
  { message: 'hello' },
  'ducks'
];

const splitOutOddNumbersAndRemoveObjectsEntirely = value => {
  if (typeof value === 'object') {
    return;
  }

  if (value % 2 === 0) {
    return true;
  }

  if (value % 2 === 1) {
    return false;
  }

  return value;
};

console.log('testData before:', testData);

const output = testData.filterSpliceSort(splitOutOddNumbersAndRemoveObjectsEntirely);

console.log('testData after:', testData);
console.log('return value:', output);