Functional components allow to have this reference

[riwu]

• I have reviewed the documentation
• I have searched existing issues
• I am using the latest React Native version

Environment

Environment:
OS: macOS Sierra 10.12.6
Node: 9.10.1
Yarn: 1.5.1
npm: 3.10.10
Watchman: 4.7.0
Xcode: Xcode 9.2 Build version 9C40b
Android Studio: 3.0 AI-171.4443003

Packages: (wanted => installed)
react: 16.3.1 => 16.3.1
react-native: 0.55.2 => 0.55.2

Steps to Reproduce

const Example = props => (
  <Button
    title="Click"
    onPress={() => {
      this.count = (this.count || 0) + 1;
      props.setCount(this.count);
    }}
  />
);

class App extends React.Component {
  state = {
    count1: 0,
    count2: 0,
  };
  render() {
    return (
      <View style={{ alignItems: 'center', justifyContent: 'center', flex: 1 }}>
        <Example setCount={count => this.setState({ count1: count })} />
        <Text>{this.state.count1}</Text>
        <Example setCount={count => this.setState({ count2: count })} />
        <Text>{this.state.count2}</Text>
      </View>
    );
  }
}

In React.js, stateless components are not allowed to have this reference so Example would give an error on click.

In react-native, this unexpectedly behaves like a class property instead.

Both the <Example /> instances share the same this, so clicking on one button would increment this.count for both instances.

[syumai]

In bundled js file, babel declares _this and intializes with this to transpile arrow functions to es5 functions.
The content of this was the global object named DedicatedWorkerGlobalScope.
I confirmed that the same phenomenon will occur in the release build.

Since a Object (in this case, DedicatedWorkerGlobalScope) is passed,
it can have the count property and the value of its count property can be referenced.

In expo snack, it failes because global object is undefined in snack.
Here's link of snack: https://snack.expo.io/SJVB1fESm

link of a part of bundled JS: https://gist.github.com/syumai/0dbe2d8bcbc17475a211b39ec6ee4241#file-bundle-js-L17

[stale]

Hey there, it looks like there has been no activity on this issue recently. Has the issue been fixed, or does it still require the community's attention? This issue may be closed if no further activity occurs. You may also label this issue as "For Discussion" or "Good first issue" and I will leave it open. Thank you for your contributions.

[riwu]

Should this be fixed?

[elicwhite]

Babel has been updated since 0.55.2, does this repro in 0.59? I'm going to close this as the version in the original post is quite old, but if this reproes still in 0.59 then let us know and we can reopen the issue.