While implementing ShadowRealms I've also been playing with it a bit.
I'm curious about the design decision around the WrappedFunction [[Call]] internal method. That method wraps the this value; which then requires that this be either a primitive or callable.
This can lead to some surprising behaviour; for example, you cannot do setTimeout on a wrapped function object, because it explicitly sets the this value to an object, which isn't callable
var h = realm.evaluate('() => log("Heyho")')
setTimeout(h, 0); // Throws on execution.
In general, given that from the perspective of the target function, the this value will always either a primitive or a wrapped function... there's relatively little to the target function by the this value; which makes me wonder: should the [[Call]] internal method instead provide some sensible default this (i.e. undefined), or is there a way in which wrapping this is actually important?
I mean, I suppose you could imagine j = realm.evaluate('function f() { this("why"); }; f'); j.call(console.log), but I'm not sure about prioritizing that usage over the ability to pass a WrappedFunction object to APIs that may try to invoke it with a different (object) this.
mhofman
commented
2 years ago
While implementing ShadowRealms I've also been playing with it a bit.
I'm curious about the design decision around the WrappedFunction [[Call]] internal method. That method wraps the
thisvalue; which then requires thatthisbe either a primitive or callable.This can lead to some surprising behaviour; for example, you cannot do
setTimeouton a wrapped function object, because it explicitly sets thethisvalue to an object, which isn't callableIn general, given that from the perspective of the target function, the
thisvalue will always either a primitive or a wrapped function... there's relatively little to the target function by thethisvalue; which makes me wonder: should the[[Call]]internal method instead provide some sensible defaultthis(i.e. undefined), or is there a way in which wrappingthisis actually important?I mean, I suppose you could imagine
j = realm.evaluate('function f() { this("why"); }; f'); j.call(console.log), but I'm not sure about prioritizing that usage over the ability to pass a WrappedFunction object to APIs that may try to invoke it with a different (object) this.