On Sat, Apr 15, 2017 at 1:41 AM Andrea Giammarchi < andrea.giammar...@gmail.com> wrote:
> > Do you know if that's because they optimized it, or they just gave up > showing the message? > > The thing is that there are no ways to extend natives differently. > > Imagine you want a Constructor to be an Array, > `Object.setPrototypeOf(Constructor, Array)` is the only way to go because > you cannot `Object.create` a constructor. > > This is just an example of how pointless is that message, specially > because it's Babel causing it and there's no way Babel should avoid using > __proto__ where appropriate. > > TL;DR the __proto__ bails out optimizations around inferred types so that > both the object and the code dealing with such object cannot be heavily > optimized. > > At the same time ECMAScript 3rd Edition was already fast enough with > functions, classes, and stuff that has never seen the light of JIT > compilers. > > As summary, that was just an overly-agressive message that someone at > Mozilla decided was good to show to developers, the only people that would > notice, mostly the one incapable of fixing it 'cause coming from transpiled > code that inevitably needs it. > > The race to close-to-mteal performance for a scripting language can take > various unimaginable directions, showing warnings around ECMAScript > specifications shouldn't be one of these ^_^ > > Apologies for the rant and thanks for your answer. > I wonder if Symbol.hasInstance [1] would help you, which will be available when we land mozjs 52? At least, for Lang.Class and GObject.Class I found I only needed to set the prototype in order to get instanceof to work as expected. Everything else worked without setting the prototype. In the meantime you could consider using __private_GjsConstructorProxy [2] but be advised that I'm definitely going to remove that as soon as there's a real ES6 way to achieve the same thing. [1] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/hasInstance [2] https://git.gnome.org/browse/gjs/tree/gjs/jsapi-constructor-proxy.cpp?h=1.48.1#n35
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