ReferenceError: use before declaration in Edge

[jods4]

The ES2015 distribution of aurelia-bootstrapper triggers an error in Edge: "ReferenceError: use before declaration". And then the application doesn't start.

I did test before and never noticed that, so I wonder if it is an Edge regression in a recent update.
I have Edge 14.14393, I would be interested in other people testing this.

The offending code is line 126:

.then(({ Aurelia }) => startResolve(() => new Aurelia(loader)));

And Aurelia is the variable that Edge complains about.
The code above looks fine to me (given that then is called with an object that contains an Aurelia property).
It runs fine in Firefox and according to Kangax tables it should be supported in Edge as well.

Just changing the code as follows work.

.then(({ Aurelia }) => { 
  return startResolve(() => new Aurelia(loader));
});

So I'd say this is more of an Edge bug, but since it impacts us it's good to know.

[jods4]

I have a minimal repro, it requires several conditions to trigger the bug, notably nested lambdas.
This breaks Edge 14.4393:

function g(cb) { return g() }
let f = ({ x }) => g(() => x);
f({ x: 42 }); // should return 42 but throws "use before declaration".

[jods4]

Found a relevant Chakra bug: chakra-core/ChakraCore#2606.
It was opened 5 days ago, I guess it is a recent update. :(

[niieani]

We don't need the lambda, we can use function notation if it's going to help, since we only use the scope anyway (no this calls). I'd say we can re-release with a workaround.
Good catch, by the way!

[jods4]

The bug is not hard to work around as it's very sensible to syntax. Even just adding braces (block) make it vanish.

If we publish a fix the hardest part is making sure minifiers don't simplify the syntax back to broken. For instance, if we add braces or function I would expect a minifier to remove them...

It was not a hard catch as unfortunately now Aurelia ES6 does not run at all in Edge. 😦

[jods4]

@EisenbergEffect do you want to publish a fix? I can PR one if you want to.

[EisenbergEffect]

Oh, definitely. If you send a PR I'll get it out today.

[jods4]

@EisenbergEffect The fix is in the linked PR, it works for me.

[EisenbergEffect]

Merged.

[EisenbergEffect]

Release coming in a few minutes.