@connect + contextType breaks with React 16.6

[Philipp91]

(I can provide a reproducible example if there's a simple test project that I can base it on.)

Essentially, I'm using React 16.6 and doing this:

const MyContext = React.createContext();

@connect(...)
class MyComponent extends React.Component {
    static contextType = MyContext;
    render() {
        return <div>Hello {this.context}</div>;
    }
}

ReactDOM.render(<MyContext.Provider value="world"><MyComponent/></MyContext.Provider/>, ...);

And it fails with an error. In my concrete example, the value isn't "world" of course, but it happens to be undefined, so I'm getting a TypeError: cannot read property 'store' of undefined here because context===undefined. I guess if I were to pass "world" as the context, it would instead fail the invariant just below.

The problem is that the <Connect(MyComponent)> component gets its context populated based on my static contextType, even though it's setting its own legacy context for the usual redux plumbing. But the new context takes precedence. This happens because <Connect(MyComponent)> declares the legacy contextTypes and additionally hoists the contextType from the nested component. This is ultimately a bug in the hoist-non-react-statics library and I have already sent a fix there: mridgway/hoist-non-react-statics#62

Please let me know if you disagree with the fix. In case they don't merge it soon, react-redux could work around the issue by doing something like this (I can send a PR):

const hoisted = hoistStatics(Connect, WrappedComponent);
delete hoisted.contextType;
return hoisted;

[markerikson]

This is likely due to one of the known bugs in React where mixing legacy context and createContext cause things to work wrong. Also, while it may not be directly related, we don't recommend or support using connect as a decorator.

If there's an easy fix, we can potentially look at it, but otherwise my advice is to avoid using contextType on a component until React-Redux v6 is out, and you've upgraded to that.

[DJTB]

Can confirm using the decorator is not related here.
Using connect() around a class with static contextType = myContext is resulting in the same undefined store error.

[CrOrc]

Until react-redux v6 is released the easiest workaround is to wrap component with contextType into function component

const MyContext = React.createContext();

class MyComponent extends React.Component {
    static contextType = MyContext;
    render() {
        return <div>Hello {this.context}</div>;
    }
}
const MyConnectedComponent = connect(...)(props=><MyComponent {...props/>)

[Philipp91]

Yeah, the connect() remark was just an fyi upon reading my code, right? I tried to find more information on this, but couldn't find any (official or unofficial) recommendation about this with a quick web search.

The fix has been merged upstream and is released in hoist-non-react-statics:3.1.0. So react-redux could be fixed by bumping the package-lock.json here and releasing a new version. I'm not sure if NPM allows users to override the hoist-non-react-statics version in their own (outer) package.json somehow.

[timdorr]

The package-lock.json files aren't provided in npm packages, nor are they used when installing. So, as long as another dependency isn't blocking the upgrade, you can use that version with react-redux.

[markerikson]

Looks like hoist-non-react-statics@3.1.0 ought to fix this: mridgway/hoist-non-react-statics#62 .

Tim, can we get that into a 5.1.1 along with the isPlainObject fix?

edit

derp, I should read things more carefully. Someone said 3.1.0 already

@timdorr , we have a direct dep on h-s-n-r@^3.0.1 currently. Can we at least bump that with the next build we release?

[timdorr]

Adding this to 5.1.1

[empav]

Any news? Using redux and connect a parent component to it, the static contextType does not work for me either:
react 16.7.0
react-dom: 16.7.0
react-redux: 6.0.0

[markerikson]

@epavan : Please provide a project that specifically demonstrates this problem.

[empav]

Can't access this.context.object at all! Tried also the nonstatic version.

/* eslint no-unused-vars:"off" */
import React, { Component } from 'react';
import ReactDOM from 'react-dom';

const SomeContext = React.createContext();

class Provider extends React.Component {
  state = {
    object: { say: 'Hi there' }
  };

  render() {
    return <SomeContext.Provider value={this.state}>{this.props.children}</SomeContext.Provider>;
  }
}

class Workareas extends React.Component {
  static contextType = SomeContext;

  render() {
    return (
      <Provider>
        <pre>Context value: {JSON.stringify(this.context)}</pre>
      </Provider>
    );
  }
}

export default Workareas;

[markerikson]

@epavan : can you please turn that into a CodeSandbox project that's runnable?

[empav]

I'm doubtful with some incompatibility with react-router 3 which uses context to provide router/route params. I'll try to codesandbox it.