diff.js

// Create a function that accepts 2 arguments. Both arguments
// should be arrays of integers. The function should return the
// differences between the first and second arrays.
//
// Example:
//
//   Array One [1, 2, 4]
//   Array Two [2, 3]
//
//   [1, 2, 4] => [2, 3]
//
//   Added: 3
//   Removed: 1, 4

(function(a, b) {
  'use strict';

  var removed = a.filter(function(value) {
    return b.indexOf(value) < 0;
  });

  var added = b.filter(function(value) {
    return a.indexOf(value) < 0;
  });

  var merged = a.filter(function(value) {
    return ~b.indexOf(value);
  }).concat(added);

  // Would normally be a return value, ie. `return results`
  console.log(
    "\nAdded:", added,     // => [ 3 ]
    "\nRemoved:", removed, // => [ 1, 4 ]
    "\nMerged:", merged    // => [ 0, 2, 3 ]
  );
})([0, 1, 2, 4], [0, 2, 3]); // (original array, new array)