Merge pull request #18 from reactjs/gaearon-patch-1

Add June 2 notes

Author: gaearon

2016-06/june-02.md

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+## June 2 ([discuss](https://github.com/reactjs/core-notes/pull/18))
+
+### Attendees
+
+* [Ben](https://twitter.com/soprano) (React)
+* [Jim](http://github.com/jimfb) (React)
+* [Keyan](https://twitter.com/keyanzhang) (React, intern)
+* [Paul](https://twitter.com/zpao) (React)
+* [Sebastian](https://twitter.com/sebmarkbage) (React)
+* [Shayne](https://github.com/shayne) (React Native)
+* [Tom](https://twitter.com/tomocchino) (React)
+
+### Getting Rid of `PureRenderMixin`
+
+* This is one of the most commonly used mixins.
+* We need to have a good story around applying it to classes and SFCs (**stateless functional components**).
+* Let’s consider a few alternatives.
+
+#### Proposal 1: `PureComponent` and heuristics for SFCs
+
+* Create `React.PureComponent` base class (kinda like a class with `PureRenderMixin`).
+* Make SFCs “inherit” their purity from the closest class-based parent.
+* This works because if the class above is pure, SFC wouldn’t re-render anyway.
+* Implemented in [#6914](https://github.com/facebook/react/pull/6914) with some additional explanation [here](https://github.com/facebook/react/pull/6914#issuecomment-222364942).
+
+##### Concerns
+
+* Any heuristics based model will probably not work in 100% of cases, and could cause confusion.
+* If you pass children through, you don’t know anything about them, including whether they use mutation.
+
+##### Potential Mitigations
+
+* Warn if a `PureComponent` takes in a child element (or child element which changes).
+* In dev mode, do dry-run reconciliation past all `shouldComponentUpdate`s and warn if `shouldComponentUpdate` lied to React.
+
+#### Proposal 2: SFCs Always Shallowly Compare Props
+
+* Effectively a `PureRenderMixin` on every SFC.
+
+##### Concerns
+
+* Means that component authors generally can’t / shouldn’t use SFCs because `PureRenderMixin` shouldn’t be used with components that take children.
+* Intuitively, people expect SFCs to behave like functions. The bailout would be surprising, and there isn’t a particularly good way of discovering why the function isn’t behaving like a normal JavaScript function.
+* Performance. It’s not clear that adding `PureRenderMixin` to every SFC would actually improve overall performance (because it means extra reads/compares, retaining objects longer and into subsequent GC generations, etc).
+
+#### Proposal 3: `createPureElement`
+
+* Provide some flag on components at the calling side to denote that they should be pure.
+* This would tell React to effectively “use `PureRenderMixin`” on that particular instance, *not all instances*.
+* Many syntax possibilities: `pure={true}`, or `<*Component />`, `React.createPureElement()`, etc.
+
+### ES Class Progress
+
+* [Ben](https://twitter.com/soprano) is leading the effort to port Facebook codebase to ES classes.
+* We plan to enable property initializer syntax internally, and codemod all methods except lifecycles to it.
+
+------------
+
+Please feel free to discuss these notes in the [corresponding pull request](https://github.com/reactjs/core-notes/pull/18).