See Phab:rP23773 for a situation where we are not correctly picking up JS errors.
The above is probably incorrect and soon outdated -> JS_ReportError was mangling stack traces apparently.
My suggestions are thus:
One option is throwing a C++ exception, since the boolean return value is used to indicate something different (see D2727). It's a typical 'trilean' -> true, false, ERROR. No other GUI code that I know of throws an exception, so it seems like something that shouldn't be looked at in a vacuum -> for another day.
Another alternative is calling JS_IsExceptionPending after each call to a ScriptEventWithReturn. This seems more productive, but less systematic, and somewhat invasive.
It would probably be a better direction to have LOGERROR (or a variant thereof) also check for pending JS exceptions, make sure JS reports them correctly, then moves on.
