Generator syntax

This syntax is the LazyPromise equivalent of async-await. It lets you take advantage of JavaScript control flow statements, and as with chained operators, you get automatic cancellation. Just use generator functions instead of async functions, and yield* instead of await:

// Type inferred as LazyPromise<number>
const lazyPromise = fromGen(function* () {
  while (true) {
    // Type inferred as number | undefined
    const value = yield* new LazyPromise<number | undefined>(...);
    if (value !== undefined) {
      return value;
    }
  }
});

In the case of native promises, if you await promise, and promise rejects with error, it’s as if in place of await promise you had throw error. It works in exactly the same way when you have yield* lazyPromise and lazyPromise rejects.

If you yield* to a lazy promise inside a try or catch block, and the whole flow is canceled while waiting for that lazy promise, the finally block will not get executed. Similarly, the .finally method will run its callback if the lazy promise resolves or rejects, but not if it’s unsubscribed before settling.