JS async await不等待也不阻塞进程

Question

I want to acheive something like this:

setTimeout(function() {
   console.log("1");
}, 3000);

console.log("2");

And I want 1 to be logged before 2.

I have tried this:

async function a() {
  var v = await setTimeout(function() {
    console.log("1");
  }, 3000);
  console.log("2");
}

a();

And I have tried more things but nothing works. How do I tell JS to WAIT until one thing is done, then go to next thing. Please, WITHOUT THE USE OF PROMISE!

Thanks.

Answer 1

There is no way to use await/async without promises. The whole functionality is based on promises. Sometimes it may seem like it works without promises, but that's only because some other function is returning a promise.

The best you can do is create a simple wait function that returns the promise and await it. For example:

 wait = (time) => new Promise(resolve => setTimeout(resolve, time)) async function test(){ console.log("one") // Pause await wait(2000) // continue console.log("two") } test() 

There is nothing (that you should be using) in javascript that will suspend the event loop and wait. Part of writing JS is learning to work with this fact.

Answer 2

Your code doesn't work because setTimeout doesn't return a Promise . Here's a little helper function that actually returns a Promise and achieves what you wanted to do:

const sleep = ms => new Promise(res => setTimeout(res, ms));

Use it like this:

async function a() {
  await sleep(3000);
  console.log("1");
  console.log("2");
}

a();

This waits for 3000 milliseconds, logs "1" and then "2" . I don't get why you would need to wait before something happens, but I just "translated" your code to actually use Promises.