[lib.d.ts BUG] navigator.mediaDevices.getUserMedia returns PromiseLike (actually returns a Promise)

[jhm-ciberman]

TypeScript Version: atom-typescript

Code

var a = navigator.mediaDevices.getUserMedia(options);
a.catch( () => console.log ); 
//ERROR: 'catch' does not exists on type 'PromiseLike<MediaStream>'

Expected behavior:
Acording to MDN, navigator.mediaDevices.getUserMedia returns a Promise (with a catch method), not a PromiseLike (without catch method).

Actual behavior:
navigator.mediaDevices.getUserMedia returns a PromiseLike<MediaStream>
It needs to return a Promise<MediaStream>

[hongbo-miao]

I am using TypeScript 2, and got same error, originally asked on Stack Overflow

maiermic's answer:

The build-in library dom declares the issue causing definition (see lib.dom.d.ts):

getUserMedia(constraints: MediaStreamConstraints): PromiseLike<MediaStream>;

whereas @types/webrtc declares your expected definition (see MediaStream.d.ts):

getUserMedia(constraints: MediaStreamConstraints): Promise<MediaStream>;

[mhegazy]

To fix this we will need to put Promise in lib.d.ts; but looks needed.

[zhengbli]

So we should get an ES6 version of the dom.generated.d.ts that replaces all PromiseLike with Promise, when the user is either targeting es6+ or somehow speficied in the --lib compiler options.

[mhegazy]

We still need promislike. Let's talk about this. Maybe we should just make es6 the default.

[prencher]

Has there been any movement on this? This is a long standing issue at this point.

[aluanhaddad]

ES2015 as the default might make sense, there are already a lot of features in lib.d.ts that are not supported by a number of browsers in wide use. But there is also a lot of stuff in there that would be confusing for ES5.1 users and since TypeScript does not include an official polyfill, which I might add is a very good thing, I'm not sure if this is the right way to go.

[Nek-]

So the quick fix is the following:

# TS 2.x only
npm install --save @types/webrtc

(just sayin for newcomers on the issue)

[prencher]

@Nek- No, that does not fix the issue. Inside of VS Code it correctly resolves the types from @types/webrtc, but in an actual build, TypeScript uses the one from lib.d.ts.

We use that types package and we had to explicitly add as Promise<foo> casts anywhere we use these APIs to make TypeScript not error.

[alcfeoh]

Any known workaround for this issue? For now I just don't catch exceptions and let them land in the browser console, which gets the job done but still doesn't seem right as I should really be able to catch it from my Promise.

[kjackson87]

I'm having this issue as well. @prencher could you provide a bit more context for your as Promise fix?

[mhegazy]

Duplicate of #13947

[mhegazy]

I should clarify, the generator converts Promise to PromiseLike, which is incorrect.