Apply component spec + mixins specs deterministically

[zpao]

Right now we don't do this consistently, so you could have behavior that varies depending on where you put the mixins key in your class spec. That's not great.

Here's an example: http://jsfiddle.net/zpao/9sW7n/ (using master)

var Mixin = {
  componentDidMount: function() {
    console.log('Mixin');
  }
};

var CompA = React.createClass({
  mixins: [Mixin],
  componentDidMount: function() {
    console.log('CompA');
  },
  render: function() {
    return <span>A</span>;
  }
})

var CompB = React.createClass({
  componentDidMount: function() {
    console.log('CompB');
  },
  mixins: [Mixin],
  render: function() {
    return <span>B</span>;
  }
})

This outputs:

"Mixin"
"CompA"
"CompB"
"Mixin"

I think we should consistently behave like CompB (component, then mixin methods) but @yungsters disagrees. Any other opinions. @petehunt @sebmarkbage @jordwalke

Potentially interested @gaearon (once we figure out which way we go)? This is relatively contained and testable but it does take you right into core.

[sophiebits]

Doing mixins first is more intuitive to me because that's normally how people write the specs (in my experience, at least).

[gaearon]

Hi, thanks for the mention. I'd like to take on this if nobody minds.
I agree with @spicyj that calling mixins first is more intuitive.

[sophiebits]

@gaearon Go for it! Let me know if you have any questions; I'm happy to help.

[gaearon]

OK great. I'll try to do it tomorrow.

[gaearon]

@zpao @spicyj

Mention me if there's something else I can take. I liked that although this task had a small scope, it introduced me to the way createClass actually works and how spec transforms into a component instance. It would be cool if I could take a few small tasks in other areas (rendering, batching) that introduce me to these areas.