WeakMap.prototype.set should return a TypeError

[jasonmit]

https://tc39.github.io/ecma262/#sec-weakmap.prototype.set

Related: thoov/ember-weakmap#3

[mixonic]

@jasonmit I'm unsure is this is a tradeoff between spec adherence vs. performance. /cc @stefanpenner

[stefanpenner]

Ya I'm curious as to the performance impact, if we do decide to keep the assertion around in prod, the following may be the most performant variant. (largely focusing on keeping AST size to a min, so allow for more inlining).

var type = typeof obj;
if (obj && (type === 'object' || type === 'function')) {
   metaFor(obj).writableWeak()[this._id] = (value === undefined ? UNDEFINED : value);
   return this;
}

invalidKey()

Obviously this may just be pre-mature optimization, but I am genuinely curious as to the impact. https://github.com/stefanpenner/do-you-even-bench may be used to quickly test the differences

My guess is metaFor(obj).writableWeak()[this._id] will overshadow the costs of the assertion anyways..

[homu]

☔ The latest upstream changes (presumably #13658) made this pull request unmergeable. Please resolve the merge conflicts.

[stefanpenner]

cc @jasonmit