Ability to extend static Event interface

[Busyrev]

Main idea

Moved EventConstructor to separate interface for better extensibility.
Before this patch Event was declared with literal:

declare var Event: {
    prototype: Event;
    new(typeArg: string, eventInitDict?: EventInit): Event;
    readonly AT_TARGET: number;
    readonly BUBBLING_PHASE: number;
    readonly CAPTURING_PHASE: number;
};

in that case there is no ability to add static properties to Event using declaration merging.

Moved EventConstructor to separate named interface, now anyone can extend it in own project using declaration merging, same idea as ArrayConstructor declaration:

interface EventConstructor {
    prototype: Event;
    new(typeArg: string, eventInitDict?: EventInit): Event;
    readonly AT_TARGET: number;
    readonly BUBBLING_PHASE: number;
    readonly CAPTURING_PHASE: number;
}

declare var Event: EventConstructor;

As far as I know, this change made no side effects for anyone.

And some additional questions

1. Strange changes in dom.generated.d.ts

src\lib\dom.generated.d.ts git shows that 1144 lines added and 1143 removed, but TortoiseGitMerge shows only some lines changed(event declaration). Github shows many lines changed. I`m using Windows 10 may be it is line ending problem, but file is autogenerated, what should i do to make diff clear?

2. const vs var

Array declared:

declare const Array ...

But Event declared:

declare var Event ...

Should all declarations be const or var?

3. Different declarations fo Event in different files

Declaration of Event declared in tests\lib\lib.d.ts:

declare var Event: {
    prototype: Event;
    new(type: string, eventInitDict?: EventInit): Event;
    AT_TARGET: number;
    BUBBLING_PHASE: number;
    CAPTURING_PHASE: number;
}

differs from Event declared in all another d.ts files:

declare var Event: {
    prototype: Event;
    new(typeArg: string, eventInitDict?: EventInit): Event;
    readonly AT_TARGET: number;
    readonly BUBBLING_PHASE: number;
    readonly CAPTURING_PHASE: number;
};

shoul this declarations be equal? By meaning they are equal now.

4. Convert another declarations?

Would it be better to convert all delare var/const declarations with literal type to separate named types?

May be some questions better to convert to separate issues for discussion?

[mhegazy]

Thanks for your PR. these files are not manually edited, they are auto-generated from a script in . You can find more information about contributing lib.d.ts fixes at https://github.com/Microsoft/TSJS-lib-generator.

Changes should be done in https://github.com/Microsoft/TSJS-lib-generator instead.

Please find more information at: https://github.com/Microsoft/TypeScript/blob/master/CONTRIBUTING.md#contributing-libdts-fixes.

For future references, please file an issue first to track changes.

[mhegazy]

1. Strange changes in dom.generated.d.ts

the files are auto generated.

2. const vs var

var is used for back compat purposes, to allow redeclaration of the variable. we do not expect Array would be redefined, but other HTML* elements are frequently redefined in DT for new proposals that are not in the lib, e.g. WebGL, WebAudio, etc..

3. Different declarations fo Event in different files

The files are generated by concatenating multiple sources.

4. Convert another declarations?

No, creating new types pollute the global namespace, and we would like to keep these to a minimum

[mhegazy]

More importantly, we need some justification for adding the new type. what is the scenario you are trying to achieve, and why it is not working today. Please file an issue and these scenarios in it.