JS array diff

array-diff.js

function arrayDiff(a1, a2) {
  var diff = {};

  for (var i = 0; i < a1.length; i++) {
    diff[a1[i]] = true;
  }

  for (var i = 0; i < a2.length; i++) {
    if (diff[a2[i]]) {
      delete diff[a2[i]];
    } else {
      diff[a2[i]] = true;
    }
  }

  return Object.keys(diff);
}

function isArrayDiff(a1, a2) {
  return arrayDiff(a1, a2).length > 0;
}