Object.keys

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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!

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Discussion

  1. Franz

    Why don’t you use this:

    for (let trait in person){console.log(trait)}
    • Kay.L

      @Franz,
      for..in iterating over NON own properties.

    • Proqz

      Not very well supported http://caniuse.com/#feat=let

    • Proqz

      Also would iterate over prototype properties.

    • Abis Mal

      The for each...in statement is deprecated as the part of ECMA-357 (E4X) standard. E4X support has been removed, but for each...in will not be disabled and removed because of backward compatibility considerations. Consider using for...of instead. (Please refer to bug 791343.)

  2. Also: Use const, not let. The loop creates a new context in each iteration, the loop variable therefore is constant unless your loop-code changes it.

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