Add ability to extend/replace built-in constructor declarations (eg. CustomEvent)

[DanTup]

I raised this on Codeplex; but I don't believe it's supported. I'm not sure which of the two referenced cases are most appropriate, so thought it best to raise as I'd posted originally. If this overlaps with an existing GH issue; please let me know.

Original Codeplex issue: http://typescript.codeplex.com/workitem/2531

I'm using the CustomEvent polyfill from here:
https://developer.mozilla.org/en/docs/Web/API/CustomEvent

DOM4 specifies a CustomError constructor that takes a string type and an (optional) custom data object:

window.dispatchEvent(new CustomEvent('doStuff', { detail: 1 }));

It seems that TypeScript will not allow this code to be compiled, it expects an argument-free constructor. I cannot figure out how to extend/replace CustomEvent to allow it. There's an answer on SO that seems to explain why:

http://stackoverflow.com/questions/17571982/dispatching-custom-events

it says:

If the CustomEvent definition was purely an interface, you would be able to extend it thus:
(blah)
But the CustomEvent constructor is actually defined in a variable declaration, which you can't extend

My codebase is currently only around 40 lines of JavaScript, and already I can't make it work in TypeScript :(

I think TypeScript needs to be able to support things like this; Browsers will never have identical implementations and the specs are moving targets. We need to not have our hands tied by decelerations in lib.d.ts with the only way around them being to have a local hacked copy of lib.d.ts!

Note: I actually think the current CustomEvent decleration in TypeScript is kinda useless because Chrome doesn't even allow you to call "new CustomEvent()"; it'll crash. Even removing it completely and forcing me to declare it seems a better option than what we have now :-/

[DanTup]

Oh; just found #182; this case might be considered a dupe of that?

[RyanCavanaugh]

Yea, I think fixing #182 would fix this issue (assuming we do it broadly, which I think we would)