Polyfill support for __proto__ in IE <= 10

[buschtoens]

Fixes #436.

This gives full support for stuff like this in IE <= 10:

Table.reopen({
  getFirstColumn() {
    return this.get('columns.firstObject');
  }
});

---

Juicy technical details

MDN on Object.prototype.__proto__

Internet Explorer

Classes (10 and below)

If you’re inheriting from a class then static properties are inherited from it via __proto__, this is widely supported but you may run into problems with much older browsers.

NOTE: __proto__ is not supported on IE <= 10 so static properties will not be inherited. See the protoToAssign for a possible work around.

babel-plugin-transform-proto-to-assign

This plugin allows Babel to transform all __proto__ assignments to a method that will do a shallow copy of all properties.

Detail

This means that the following will work:

var foo = { a: 1 };
var bar = { b: 2 };
bar.__proto__ = foo;
bar.a; // 1
bar.b; // 2

however the following will not:

var foo = { a: 1 };
var bar = { b: 2 };
bar.__proto__ = foo;
bar.a; // 1
foo.a = 2;
bar.a; // 1 - should be 2 but remember that nothing is bound and it's a straight copy

This is a case that you have to be aware of if you intend to use this plugin.

[buschtoens]

Not really sure, if these tests make a lot of sense, since we don't run CI tests for IE anyways.

Also, they mutate the Classes. This means that all following test cases have access to someStaticMethod and someMethod. This might not be a problem now (and I doubt it ever will), but it could and feels kind of dirty.

[buschtoens]

I think, I should rather write a specialized unit test for utils/fix-proto. This way, there's no mutation of global classes.

[buschtoens]

There's now a dedicated test for fixProto, asserting that ES6 classes that extend Ember.Object can be reopened after fixProto was used on them.

The testes for Column, Row and Table now merely assert that reopen and reopenClass are functions.

All these tests are pretty meaningless though, as we don't test in IE <= 10. But now we could verify regressions quickly, if someone reports this issue again. 🤷‍♂️

[offirgolan]

@buschtoens I think we should just move to pure Ember.Object in the next major release because this is kinda getting gross lol.