Repository navigation
TypeError: Cannot read property 'bind' of undefined when using Flow #5176
Description
Is this a bug report?
Yes
Did you try recovering your dependencies?
Yes
Which terms did you search for in User Guide?
flow bind
Environment
Environment:
OS: macOS Sierra 10.12.6
Node: 10.11.0
Yarn: Not Found
npm: 6.4.1
Watchman: 4.7.0
Xcode: Xcode 9.2 Build version 9C40b
Android Studio: Not Found
Packages: (wanted => installed)
react: ^16.5.2 => 16.5.2
react-dom: ^16.5.2 => 16.5.2
react-scripts: 2.0.1 => 2.0.1
Steps to Reproduce
- Create a component like this one
class Foo extends React.Component {
constructor(props) {
super(props)
this.foo = this.foo.bind(this)
}
foo: () => ()
foo() {}
render() { return <div /> }
}- Run the tests for
Foo TypeError: Cannot read property 'bind' of undefined
Expected Behavior
The file should run in the tests
Actual Behavior
I think Flow's syntax is confusing the tests. Note that this same code was working in the previous version of CRA
Reproducible Demo
Simply clone https://github.com/Gpx/cra2-bind and run the tests
Activity
gaearon commentedon Sep 30, 2018
This is because Babel 7 changed the behavior of class properties so that an empty “definition” like this is treated as assigning
undefined. AFAIK this is closer in behavior to the latest specification.We’ll need to mention this in migration notes.
Still I’m not sure if this is correct. We’ll need more eyes on this.
Some discussion: babel/babel#8417.
Apparently this could solve it? xing/hops@9cf7791
Maybe our preset should do this.
Gpx commentedon Sep 30, 2018
The thing is that Flow is asking me to add a type definition to
fooand I don't know how else to do itgaearon commentedon Sep 30, 2018
Yeah, I understand. We'll need to dig deeper into this.
Gpx commentedon Sep 30, 2018
Ok, thanks. Let me know if I can help somehow
bugzpodder commentedon Sep 30, 2018
@Gpx try this. This uses the flow commenting method. Obviously not ideal but it should provide with a workaround.
Gpx commentedon Sep 30, 2018
@bugzpodder yep, that works, unfortunately, in my app, we use prettier which converts comments into standard type definitions. I think we'll wait to update CRA until this issue has been closed