fix retrieval of "this" object in ControllerEngine::beginTimer

[Be-ing]

This will facilitate using timers in Components, for example to implement alternate actions on double button presses or long presses.

[daschuer]

32bit windows build stops in the middle of an unrelated test. I assume it is a timeout.
LGTM

[rryan]

I'm wondering whether this might have unintended consequences -- what if the function passed to beginTimer has a 'this' specifically bound to it via Function.prototype.bind by the programmer?

It's too bad we can't use ES6 arrow lambda (which would use 'this' from the scope it was created in) until QtScript supports ES6. I wonder whether it's better to suggest scripters use Function.prototype.bind to work around this instead of adding more 'this' hackery into the ControllerEngine itself.

[Be-ing]

It's too bad we can't use ES6 arrow lambda (which would use 'this' from the scope it was created in) until QtScript supports ES6.

Yeah, last I checked no one was actively working on supporting ES6 in QtScript. :/

I wonder whether it's better to suggest scripters use Function.prototype.bind to work around this instead of adding more 'this' hackery into the ControllerEngine itself.

This PR only fixes the behavior as it was intended to work (but never did). I don't think script authors should have to do an extra step of binding the function to use this as expected, but I don't know how to how to detect if the script author has bound the function. Perhaps Mixxx could check if the function's this object is the same as that returned by getThisObjectInFunctionCall, and if it isn't, use the function's bound this object?

[rryan]

Yeah, last I checked no one was actively working on supporting ES6 in QtScript. :/

I know! Let's add Node and Babel as a Mixxx dependency and transpile the ES6 to ES5 on the fly .

[Be-ing]

I know! Let's add Node and Babel as a Mixxx dependency and transpile the ES6 to ES5 on the fly .

Someone actually tried that... I haven't seen any activity from them since...