[3.0] Saving the value of 'this' is broken in class constructor but works with transform-es2015-classes

[Jessidhia]

The code in the following gist (which happens to be based on the example at facebook/react#7094 (comment)) explains the issue in more detail:

https://gist.github.com/Kovensky/0ce87560e4b3c93cd77475fdcf94b610

Using [email protected]. Note that the component in that gist is not inside an AppContainer, but the "real world" version of it ultimately is, and that one also has the same error behaviour.

The same problem also happens when using transform-class-properties and arrow function properties, as they're bound at construction time.

[Jessidhia]

This seems related to #242. If it's not supported at all, I wonder, then, why did it (appear to?) work when transform-es2015-classes was used...

[jkeljo]

I'm seeing this as well. The React docs recommend this pattern of reassigning functions in the constructor for a couple of purposes:

• binding handlers in ES6 classes
• using PureRenderMixin in ES6

But even the presence of react-hot-loader is enough to break the pattern (you don't actually need to make a code change). From playing around in the debugger, it looks like react-hot-loader is cloning the objects in a way that doesn't update the binding of already-bound member functions.

I created a repro repo here before I realized that this was the same issue.

[MarshallOfSound]

Came across this today while doing some work integrating react-hot-loader into a pure Electron dev workflow. In Electron you only need to target latest stable Chromium which means that classes are already implemented natively. This issue is much more prominent in that space because people just don't use the class transform as it isn't required.

If someone can point be in a good direction I'll be happy to dive into this at some point and get it sorted.

[wkwiatek]

@MarshallOfSound it's the issue of react-proxy. If you wanted to start with this, just try to do a simple proxy object (with react-proxy@next), and play with a dubugger. We'll dive into react-proxy more once we have docs ready for RHL as it's the highest prio now.

[MarshallOfSound]

@wkwiatek OK so I spent a while inside of react-proxy and like half got it working, it's insanely complex so this could take a while I feel 😆

[merges]

Is there a workaround for those of us who are experiencing this issue today?

[penx]

I had this issue when trying to switch from babel-preset-es2015 to babel-preset-env. Adding transform-es2015-classes to the included transforms resolved it for me:

presets: [
  ['env', {
    targets: {
      chrome: 60
    },
    include: ['transform-es2015-classes']
  }],
  'stage-1',
  'react'
],
plugins: ['react-hot-loader/babel'] 

[gregberge]

This is a known problem, we have to update babel plugin to handle native classes. Help welcome!

[can-cc]

+1
wait update

[ChuckJonas]

Also looking for a fix here!

[kyleramirez]

+1
Thanks for being on this. Waiting patiently for an update.

[gregberge]

Fixed in v4. Also added a modern example.