我可以在JavaScript中强制解决承诺以等待结果吗？

Question

This question is somewhat academic in that I don't have a real need to do this.

I'm wondering if I can force the resolution of a promise into a returned value from a function such that the function callers are not aware that the functions contain promised async operations.

In .NET I can do things like this by using functions on Task[] or return Task.Result which causes the caller to await the completion of the task and callers won't know or care that the work has been done using tasks.

Answer 1

If you're using ES6 you can use a generator to make code like this. It essentially comes close to 'blocking' on the promise, so you have the appearance of a long-running method that just returns the value you want, but async/promises live under the covers.

let asyncTask = () =>
  new Promise(resolve => {
    let delay = Math.floor(Math.random() * 100);

    setTimeout(function () {
      resolve(delay);
    }, delay);
  });

let makeMeLookSync = fn => {
  let iterator = fn();
  let loop = result => {
    !result.done && result.value.then(res =>
      loop(iterator.next(res)));
  };

  loop(iterator.next());
};

makeMeLookSync(function* () {
  let result = yield asyncTask();

  console.log(result);
});

More explanation and the source available here: http://www.tivix.com/blog/making-promises-in-a-synchronous-manner/

Here is the code compiled on Babeljs.io