Equivalent of React's PureRenderMixin about scalajs-react HOT 9 CLOSED

What this does is configure shouldComponentUpdate to compare equality of props & state.
Concept is good, JS implementation isn't what we want for Scala.

Better would be to add something applicable via ReactComponentB.configure that uses scalaz.Equal for comparison, or plain == for dangerous people.

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Bloody callbacks stuff up Props equality... Might need to introduce a mechanism for callback identity and comparison.

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+1 First thing i was sad about.

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A better equivalent of this will be in the next version of scalajs-react.
(Better because the JS version 1) has an issue, 2) doesn't play with with Scala, 3) give no guarantees).

Release should be out in under a month.

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Awesome!

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Right now i'm using this workaround.

implicit class ReactCompBExt[Props, State, Backend](comp: ReactComponentB[Props, State, Backend]) {    
    def pure = shouldUpdateS { case (was, toBe) => was != toBe }

    def shouldUpdate(f: ((Props, Props)) => Boolean) = comp.shouldComponentUpdate(
      (scope, newProps, _) => f(scope.props, newProps))

    def shouldUpdateS(f: (((Props, State), (Props, State))) => Boolean) = comp.shouldComponentUpdate(
      (scope, newProps, newState) => f((scope.props, scope.state), (newProps, newState))
    )
  }

I could say nothing about performance yet though

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Using universal equality is dangerous in that when you, maybe now, maybe later, slip something in your props or state for which == doesn't hold, you're not going to know unless you pay close attention at runtime and then investigate back. The Scala compiler is not your friend and will not help you.

This is especially an issue when you pass callbacks around (which is the norm). How would one expect Scala to compare functions? By reference? Most callbacks will be regenerated unless you've structured them a very special way, and again, because the compiler's not involved there's no way of knowing whether you're doing it wrong and are going to break shouldComponentUpdate on every call.

It's unpleasant but it's a real issue. It's something to be aware of when using an approach like above.

I have a solution for these issues. I'll try to get it online well before the release so they can be critiqued. Feedback is always appreciated and just now looking at your snippet there's already a case I didn't touch - state comparison (I only use props comparison).

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I've created a branch for the performance management stuff that will go into 0.9.0 and added tools that address this issue.

Read all about it here:
https://github.com/japgolly/scalajs-react/blob/0.9/extra/PERF.md

This will go out in 0.9.0 in about a month's time, and close this issue.

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Closed via 9e8f5bd

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