Object.keys

I adore JavaScript objects.  Love them.  You're probably asking "well, why don't you marry them?"  Trust me:  if I could, I would.  Arrays are nice and all but object keys provide another level of structure and information that is invaluable.  For example, it's much faster search an object for a key than it is to search an array for value presence.

The way we've always iterated on an Object instance was always a for loops with a hasOwnProperty check which was ugly; Object.keys (not Object.prototype.keys) provides an array of Object properties!

var person = {
  firstName: 'David',
  lastName: 'Walsh',
  // ...
};

Object.keys(person).forEach(function(trait) {
  console.log('Person ', trait,': ', person[trait]);
});

If you work with JSON or simply raw JavaScript objects, and you haven't been using Object.keys, now is the time to ditch the old method for this elegant solution!