Deprecate `isMounted`

isMounted is already unavailable on ES6 classes, and we already have a warning saying we “might” remove them, but we don’t actually have a github issue to deprecate them. As per our discussions today, we are basically agreed that we’re going to start moving away from isMounted and deprecate it. We still need to figure out some good stories around promises (and related use cases).

This issue is to track progress toward that goal.

For background, please read:

• https://github.com/facebook/react/issues/2787#issuecomment-68738793
• https://github.com/facebook/react/issues/3417
• https://github.com/facebook/react/pull/5420#issuecomment-155577641

[istarkov]

This simple method can be used to add cancel to any promise

const makeCancelable = (promise) => {
  let hasCanceled_ = false;

  const wrappedPromise = new Promise((resolve, reject) => {
    promise.then((val) =>
      hasCanceled_ ? reject({isCanceled: true}) : resolve(val)
    );
    promise.catch((error) =>
      hasCanceled_ ? reject({isCanceled: true}) : reject(error)
    );
  });

  return {
    promise: wrappedPromise,
    cancel() {
      hasCanceled_ = true;
    },
  };
};

EDIT: Updated for correctness/completeness.

HOW TO USE

const somePromise = new Promise(r => setTimeout(r, 1000));

const cancelable = makeCancelable(somePromise);

cancelable
  .promise
  .then(() => console.log('resolved'))
  .catch(({isCanceled, ...error}) => console.log('isCanceled', isCanceled));

// Cancel promise
cancelable.cancel();

[probablyup]

Listing ways to sup-up ES6 promises to make them cancellable is besides the point. The intent should be to provide a solution that works WITH the spec rather than trying to work AROUND the spec.