Analogous to Promise.then.

onFulfilled on onRejected can return a value, a normal promise, or a CancellablePromise. So you can make a chain a CancellablePromises like this:

const overallPromise = cancellableAsyncFunction1()
    .then(cancellableAsyncFunction2)
    .then(cancellableAsyncFunction3)
    .then(cancellableAsyncFunction4)

Then if you call overallPromise.cancel, cancel is called on all CancellablePromises in the chain! In practice, this means that whichever async operation is in progress will be canceled.