Add Isolate.ThrowException(exception) support

[robfig]

Thanks for amazing project! Very exciting to be able to use v8 so easily.

I'm providing my JS script an API implemented with a Go FunctionCallback. If an error occurs, how do I signal that to the caller? Throwing a JS error seems like the correct route, but I don't see any way to do that.

For example

	
	global, _ := v8go.NewObjectTemplate(iso)
	fn, _ := v8go.NewFunctionTemplate(iso, func(info *v8go.FunctionCallbackInfo) *v8go.Value {
		// HOW TO RAISE A JS ERROR?
		return nil
	})
	global.Set("myfn", fn)

Thank you

[rogchap]

Hey @robfig
Thanks for your interest in the project.
This is unfortunately not possible 😢
I had tried to get this to work as part of the Basic Promise PR, but I had issues creating Error values... just kept crashing.
I left it out for now but plan to work on it to have it working again. Ref: #76 (comment)

[dylanahsmith]

If you use the latest changes on master, then there is now a Function.NewInstance function that can be used to call a function as a constructor (e.g. like new Error(message)). I think the only thing left is to add an Isolate.ThrowException method.

A workaround would be to execute some JS code to throw the exception (or define a function to do that). This code is on the slow path, so that may be acceptable.