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June 23 (discuss)


Update on createClass → ES classes

  • Dan finished working on a codemod for internal Facebook code that converts 800 files to remove one of the common mixins we used.
  • While doing so, Dan found an issue with inconsistent order of resolving refs during updates.
  • Ideally code should not depend on ref resolution order.
  • Unfortunately some Facebook components rely on it so for now we fixed this in React.

JSON Test Renderer

  • Ben added a new test renderer intended for snapshot testing.
  • For now, we don’t document it, as we might want to change the API.
  • We don’t want people to rely on the renderer output or test against JSON.
  • This renderer is only intended for comparing snapshots, not analyzing them.
  • It is also not clear how to dispatch events with it.
  • Jest plans to add a guide on using it later on its blog after it is more stable.

Update on 15.2.0

  • We cut the RC last week and React Native RC uses it.
  • It contains a lot of commits but not too many substantial changes.
  • Will be released within two weeks.

Update on Release Process

  • Paul started writing a maintainer’s guide to document the entire release process.
  • He ran the 15.2.0 RC release using a new tool he’s working on.
  • The process relies on us assigning semver labels (e.g. “major”, “patch”) but not specific milestones.
  • The tool will automate the release process based on those labels.
  • This should enable us to cut releases more often and let other people (e.g. React Native members) do it.

Fast Path

  • This is a hypothetical optimization Jim wanted to try.
  • What if we took functional components that render only to DOM components and precompiled them to fast path “templates”?
  • This could be an optimization specific to the DOM renderer. It would use document.createElement or cloneNode().
  • However most components use other components so it’s unclear if there are any benefits to doing this.
  • Sebastian had a more generic idea about component folding but it requires whole program analysis.
  • There is nothing conclusive here and this is not something we actively investigate.

Testing with Feature Flags

  • We currently test server rendering by enabling the client side renderer to do server side rendering (we set useCreateElement to false and re-run the suite).
  • We’d like to decouple client side from server side rendering.
  • Sebastian’s experimental “Fiber” reconciler does not yet support server rendering.
  • We need to split out server rendering before switching to Fiber.

Update on Fiber

  • This is Sebastian’s work on new core algorithm.
  • Its main goal is to render tree in chunks to avoid dropping frames on large updates.
  • It sort of works but far from feature parity.
  • Need to add support for a lot of things: lifecycle, refs, state.
  • It should be possible to keep ReactDOM and ReactDOMFiber separate.
  • It would be great to test it in isolation on a single product.

Flow with Property Initializers

Jeff will release a Flow version that infers the types from the initializers so we can write the types inline instead of specifying the type of the whole expression:

class Foo {
  doStuff = (x: number): boolean => {
    return true;

Please feel free to discuss these notes in the corresponding pull request.