Global variable `event: Event` in lib.es6.d.ts

[sod]

TypeScript Version: 2.0.3

Code

tsconfig.json includes lib es6:

{
 "compilerOptions": {
 "lib": [
 "es6",
 "dom"
 ]
 },
}

function eventHandler() {
 // typescript doesn't complain about missing event variable, because event is declared as global in lib.es6.d.ts
 console.log(event.target);
}

Expected behavior:

Don't expect event to exist on the global object. Couldn't reproduce it in Safari, Firefox or Chrome. It's always console.log(window.event); // undefined

Actual behavior:

event: Event is declared as global variable in lib.es6.d.ts
https://github.com/Microsoft/TypeScript/blob/2e7c83abc833534181d97c534bfac865cd93b1f0/lib/lib.es6.d.ts#L18680
https://github.com/Microsoft/TypeScript/blob/2e7c83abc833534181d97c534bfac865cd93b1f0/lib/lib.es6.d.ts#L20129

[kitsonk]

According to MDN it is non-standard IE/Edge property. The typings for the lib are derived from the Edge IDL, which is likely that caused it to be there.

But it does seem to be present in other browsers (I checked Chrome)

'event' in window; // returns `true`
'foo' in window; // returns `false`

I guess it should be properly typed as Event | undefined.

[sod]

Indeed. You are right. The property exists on window. But it is undefined, even in Edge 13 & IE 11.

So maybe declare var event: undefined, without the Event.

Edit: Kitson Kelly (@kitsonk) ah, it's filled while event listeners are executed in IE/edge. Hm

[kitsonk]

Yes, sorry, I meant to say that.

I suspect that IE/Edge continues to support it, though it isn't part of standards, and other browsers define it, but keep its value always undefined to avoid breaking lots of bad code, that running in strict mode, might cause an exception.

Anyways, I still suspect it is better to have it as Event | undefined.

[mhegazy]

PRs welcomed. You can find more information about contributing lib.d.ts fixes at https://github.com/Microsoft/TypeScript/blob/master/CONTRIBUTING.md#contributing-libdts-fixes.

[jarrydfillmore]

Awesome!

[alisabzevari]

I will do it 😄