Emit classes instead of vars

[saschanaz]

Now that we can extend both class instance type and static type, can we now directly emit classes? Is there any remaining blocking problems?

[sufianrhazi]

The ability to emit classes would help implement my proposed solution to the WebGL declarations' use of empty interfaces: microsoft/TypeScript#5855 (comment)

[saschanaz]

I will submit a PR if someone gives Accepting PR tag.

[RReverser]

On the other hand, emitting classes makes it much harder to extend built-in types with optional extensions, since class declarations cannot be merged together, but interfaces can.

[saschanaz]

class declarations cannot be merged together, but interfaces can.

This works:

declare class Merge {
    x: string;
}

interface Merge {
    y: string;
}

new Merge().y;

It can't extend static properties, but it never worked anyway.

[RReverser]

@saschanaz Yeah I'm trying to fix that right now actually, because ran into a problem with polyfilling static methods :) #812

[RReverser]

To be clear - I came across this issue because I'd also be happy if there was a way to reduce all that clutter and just use class, but polyfilling is quite important for Web APIs, and not being able to do it seems like a dealbreaker.

Hopefully this can be somehow fixed on TypeScript side in the future by allowing merging classes with classes, or adding static methods to interfaces or something similar.

[saschanaz]

There is a relevant issue on TS: microsoft/TypeScript#2957

[RReverser]

Actually... I've just realised that something like this might work for extending statics:

declare class Merge {
    x: string;
    static X: string;
}

interface Merge {
    y: string;
}

declare namespace Merge {
    const Y: string;
}

new Merge().x;
new Merge().y;
Merge.X;
Merge.Y;

So if we implement this, then #812 would be unnecessary.

Either option is fine by me and better than current status quo that doesn't allow any extensions, but this one would probably be even cleaner.

[RReverser]

FWIW - just so that our work doesn't conflict - I'm giving this a try.

[RReverser]

Update: I have a working implementation of this, but waiting for #813 to be merged first.