For-of Loop Default Iterator Function

Question

Consider this simple generator function defined on Object.prototype:

Object.prototype.defineProperty(Object.prototype, 'pairs', {
    enumerable: false,
    * value( ) {
        for (const key in this)
            yield [ key, this[key] ];
} });

Of course, it could be used like this:

const object = { goats_teleported: 42 };

for (const [ key, value ] of object.pairs());

But I wonder if there any way to assign pairs function to object prototype, so it will be automaticly fired in for-of loop without explicit call; just like this:

for (const [ key, value ] of object);

Any ideas?

score 2 · Answer 1 · answered Apr 28 '19 at 20:38

2

   Object.prototoype[Symbol.iterator] = function* pairs() {
     //...
   };

But be aware that this could cause side effects everywhere. This shouldn't be used in production (or at least, on your own risk ;)).

answered Apr 28 '19 at 20:38

Jonas Wilms

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score 2 · Accepted Answer · answered Apr 28 '19 at 20:38

2

Put the generator on Object.prototype[Symbol.iterator]:

Object.prototype[Symbol.iterator] = function* pairs() {
  for (const key in this) yield [ key, this[key] ];
};
const object = { goats_teleported: 42, foo: 'fooval' };

for (const [ k, v ] of object) {
  console.log(k, v);
}

answered Apr 28 '19 at 20:38

CertainPerformance

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I guess iterator can not be defined with `Object.defineProperty`, yes? – Monsieur Pierre Doune Apr 28 '19 at 20:46
I don't think so, though you can use [`Object.defineProperties`](https://stackoverflow.com/questions/36111582/is-it-valid-to-use-object-defineproperties-with-symbols) – CertainPerformance Apr 28 '19 at 20:49

score 1 · Answer 3 · answered Apr 28 '19 at 20:43

1

in ES6 you can use Symbol.iterator to define custom iterator for prototype. See here

answered Apr 28 '19 at 20:43

zoryamba

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For-of Loop Default Iterator Function

3 Answers3