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!
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Why don’t you use this:
for (let trait in person){console.log(trait)}@Franz,
for..in iterating over NON own properties.
Not very well supported http://caniuse.com/#feat=let
Obligatory https://babeljs.io/
Also would iterate over prototype properties.
The
for each...instatement is deprecated as the part of ECMA-357 (E4X) standard. E4X support has been removed, butfor each...inwill not be disabled and removed because of backward compatibility considerations. Consider usingfor...ofinstead. (Please refer to bug 791343.)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.