Warning: React component classes must extend React.Component when using ScalaJS

Question

I upgraded react to 0.14-rc1 from 0.14 beta3 , now i am seeing warnings

Warning: $c_Hello$Component(...): React component classes must extend React.Component.

but my component extending React.Component

object Hello {
  @ScalaJSDefined
  class Component extends ReactComponent[Unit, Unit] {
    def render() = React.createElement("div",null,"hello")
  }
}

no warnings in 0.14 beta3.

i think logic here is not correct ? : https://github.com/facebook/react/blob/b01af40ae64823fb963a8fa6ced3c42ae09fad55/src/renderers/shared/reconciler/ReactCompositeComponent.js#L170

in debug mode inst instanceof Component is true

The logic there is correct - warning warns when the first argument is false. So inverting the instanceof gives us what we want. What is ReactComponent in your code? Is it React.Component? Or is this something going differently in the transpilation from Scala to JS?l — Paul O'Shannessy
– Paul O'Shannessy, Commented Sep 10, 2015 at 20:54
its React.Component from reactjs ,i am just using alias for convenience in my code base . — invariant
– invariant, Commented Sep 10, 2015 at 20:55

Edgar · Accepted Answer · 2019-08-15 08:26:18Z

3

Looks like this is a scala-js bug where the .isReactClass flag doesn't get copied over. I've filed an issue there:Static class properties should be inherited

It looks like your code might also work if you change your sbt settings to use

scalaJSOutputMode := org.scalajs.core.tools.javascript.OutputMode.ECMAScript6

and then it will use native ES6 classes. But the blog post in which it was introduced suggests it's not ready for production use.

edited Aug 15, 2019 at 8:26

Edgar

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answered Sep 10, 2015 at 21:49

Sophie Alpert

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