Day 2 meeting notes

Brendan Eich brendan at
Fri Jul 30 16:21:12 PDT 2010

On Jul 30, 2010, at 3:49 PM, Oliver Hunt wrote:

>>> By overloading for(in) we are effectively saying that there will never be a simple way to iterate arrays by value directly, because no one can even extend the builtin array type be have a generator for iteration because doing so would be too fragile.
>> This "never be a simple way" is not true in JS1.7+:
>> js> Array.prototype.__iterator__ = function () { for (let i = 0; i < this.length; i++) yield this[i]; };
>> (function () {for (let i = 0; i < this.length; i++) {yield this[i];}})
>> js> for (v in [3,4,5]) print(v)
>> 3
>> 4
>> 5
>> The unstratified, ugly-named __iterator__ meta-method is the getter or factory for finding or creating an appropriate iterator. I use a generator, since it is the simplest way of writing such a factory.
> I recognised that was possible -- the problem i was saying is that you can't do that due to it polluting the global array prototype in away that effects language semantics

Yeah, and it was hardly a "simple way" as I wrote it, but these little headaches are fixable:

js> Object.defineProperty(Array.prototype, '__iterator__', {value: function () { for (let i = 0; i < this.length; i++) yield this[i]; }});
js> for (v in [3,4,5])print(v)

And put the Object.defineProperty call into some init-time code in JQuery ;-).


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