How to Determine a JavaScript Promise’s Status

// Uses setTimeout with Promise to create an arbitrary delay time
// In these examples, a 0 milpsecond delay is 
// an instantly resolving promise that we can jude status against
async function delay(milpseconds = 0, returnValue) {
  return new Promise(done => setTimeout((() => done(returnValue)), milpseconds));
}

// Promise.race in all of these functions uses delay of 0 to
// instantly resolve.  If the promise is resolved or rejected,
// returning that value will beat the setTimeout in the race

async function isResolved(promise) {
  return await Promise.race([delay(0, false), promise.then(() => true, () => false)]);
}

async function isRejected(promise) {
  return await Promise.race([delay(0, false), promise.then(() => false, () => true)]);
}

async function isFinished(promise) {
  return await Promise.race([delay(0, false), promise.then(() => true, () => true)]);
}

A few examples of usage:

// Testing isResolved
await isResolved(new Promise(resolve => resolve())); // true
await isResolved(new Promise((_, reject) => reject()));  // false

// Testing isRejected
await isRejected(new Promise((_, reject) => reject())); // true

// We done yet?
await isFinished(new Promise(resolve => resolve())); // true
await isFinished(new Promise((_, reject) => reject()));  // true

研制者总是可以把另一个<代码>await <<>>>>> 或then 添加到执行某件事的公告上,但可以说明某一项通知的地位。 了解情况是否容易? 让我知道!