Promises with typescript-2.x gives error :Cannot invoke an expression whose type lacks a call signature

debugcn Published at Dev

Akhilesh Kumar

After upgrading angular to 4.x from 2.x and typescript to 2.x started giving following error which was working fine with previous version

Cannot invoke an expression whose type lacks a call signature. Type '((onfulfilled?: (value: MediaStream) => TResult1 | Prom...' has no compatible call signatures.

My code is as following

getMediaStream(options:{video: boolean, audio: boolean}) {
    let self: Caller = this;
    return self.getUserMedia(options)
      .then(stream => {
        console.log('got our media stream:', stream);
        self.privateMedia = createObjectURL(stream);
        self.privateStream = stream;
        return stream;
      })
      .catch(() => {
        console.log('Could not get access to microphone & camera');
      });
  }

  public getUserMedia(constraints) {
    if (window.navigator.mediaDevices && window.navigator.mediaDevices.getUserMedia) {
      return window.navigator.mediaDevices.getUserMedia(constraints);
    }

    return new Promise((resolve, reject) => {
      const getMedia = window.navigator.getUserMedia;
      if (!getMedia) reject(new Error('Browser unsupported'));
      getMedia.call(navigator, constraints, resolve, reject);
    });
  }

Akhilesh Kumar

Typecasting self.getUserMedia(options) to any/Promise resolved the problem.

So I used following code and it worked:

getMediaStream(options:{video: boolean, audio: boolean}) {
    let self = this;
    return (<Promise>self.getUserMedia(options))// in place of promise 'any' or other any superclass to promise will work as well 
      .then(stream => {
        console.log('got our media stream:', stream);
        self.privateMedia = createObjectURL(stream);
        self.privateStream = stream;
        return stream;
      }).catch(() => {
        console.log('Could not get access to microphone & camera');
      });
  }

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