Merge pull request #13 from reactjs/gaearon-patch-1

Add notes for May 5

Author: gaearon

2016-05/may-05.md

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+## May 5 ([discuss](https://github.com/reactjs/core-notes/pull/13))
+
+### Attendees
+
+* [Ben](https://twitter.com/soprano) (React)
+* [Dan](https://twitter.com/dan_abramov) (React)
+* [Jim](http://github.com/jimfb) (React)
+* [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)
+
+### ReactPerf Rewrite
+
+* [Dan](https://twitter.com/dan_abramov) got his rewrite of `ReactPerf` [merged into React master](https://github.com/facebook/react/pull/6647).
+* It is mostly functionally identical to the old one but is written in a more maintainable way.
+* At Facebook, we don’t use the console `ReactPerf` API much so we’ll need community help testing this.
+* There is a corresponding [React Native PR](https://github.com/facebook/react-native/pull/7283) that depends on these changes.
+* The change removes `ReactPerf.measure()` wrappers and instead emits events (e.g. `onBeginLifeCycleTimer`).
+* Related PRs: [#6549](https://github.com/facebook/react/pull/6549), [#6612](https://github.com/facebook/react/pull/6612), [#6633](https://github.com/facebook/react/pull/6633), [#6046](https://github.com/facebook/react/pull/6046).
+* It will most likely go into `15.1.0-alpha` early next week.
+
+### TestUtils and Enzyme
+
+* Airbnb’s [Enzyme](https://github.com/airbnb/enzyme) is well maintained and supported.
+* Our [`TestUtils`](https://facebook.github.io/react/docs/test-utils.html) are not in a great shape, and most people prefer Enzyme.
+* Should Enzyme become the official `TestUtils`?
+
+#### Challenges
+
+* Ideally we want test runner to be a separate renderer.
+* Tests should run consistently and often synchronously so we don’t want to run them with [incremental reconciler](https://github.com/facebook/react/issues/6170).
+* We have no official renderer APIs yet so without `TestUtils` Enzyme would have to rely on React internals.
+
+#### Risks
+
+* If Enzyme is abandoned, we will have to maintain it.
+  * Not a big deal because this is pretty much our situation with `TestUtils` now.
+* Recommending it as an official solution might raise questions about “official solutions” to other problems.
+  * (e.g. routing, state management)
+* We don’t have guidelines for recommending something as an official solution.
+* No conclusion yet, needs more discussion.
+
+### Server Rendering
+
+* After thinking more about incremental reconciliation, [Sebastian](https://twitter.com/sebmarkbage) has some renewed interest in server rendering.
+* Whatever feature server rendering wants, it’s a good feature to have on the client as well.
+* For example, if you have a component that’s unlikely to change:
+  * Currently you have all those React internal instances in memory.
+  * But if you remove those, and are able to recover…
+  * It’s just like reviving a server rendered tree on the client.
+* Current behavior for rehydration after server rendering:
+  * It re-renders everything on the client to a string to verify the checksum, then throws it out.
+  * If it’s the same, and we need the node or instance for any reason, at that point we climb the tree and figure out what instance it corresponds to lazily.
+  * It doesn’t fix any inconsistencies it finds as it traverses back up.
+  * This is what [@aickin](https://github.com/aickin) is trying to change in his [pull request](https://github.com/facebook/react/pull/6618).
+* What does [#6618](https://github.com/facebook/react/pull/6618) help with?
+  * We can loosen constraints on validation.
+  * Markup doesn’t have to be character for character equivalent.
+  * [Ben](https://twitter.com/soprano) has [concerns](https://github.com/facebook/react/pull/6618#issuecomment-217321531) about it.
+
+### CSS Fallback Values
+
+* We don’t have a way of letting people specify fallback values for vendor prefixes.
+* People ask for something like this: `display: ['-webkit-box', '-moz-box', '-ms-flexbox', '-webkit-flex']`.
+* Using arrays for this precludes supporting something like `margin: [0, 0]` in the future.
+* We could use an opaque data structure for this, e.g. `ReactDOM.CSS.multi('-webkit-box', '-moz-box', ...)`.
+* There’s a proof of concept in [#6701](https://github.com/facebook/react/pull/6701).
+* Still needs more bikeshedding on the name but the idea is sound.
+* We might want to look at autoprefixing again the next time we approach inline styles in the future.
+
+------------
+
+Please feel free to discuss these notes in the [corresponding pull request](https://github.com/reactjs/core-notes/pull/13).