javascript - 关于javascript异步函数的 'pending'和 'fulfilled' promise

Question

async function pending() { 
  return new Promise((resolve, reject) => { resolve(1) });
}

async function fulfilled() {
  return 1;
}

function promiseState(p) {
   return Promise.race([ Promise.resolve(p).then(() => "fulfilled", () => "rejected"), Promise.resolve().then(() => "pending") ]);
}

promiseState(pending()).then(s => { console.log(s); });        // pending
promiseState(fulfilled()).then(s => { console.log(s); });      // fulfilled

pending().then(r => { console.log(r); });        // 1
fulfilled().then(r => { console.log(r); });      // 1

有什么不同？

我什么时候应该在异步函数中使用'return new Promise(...'？为什么？

Answer 1

相同与不同

function pending() { 
  return Promise.resolve(Promise.resolve(1));
}

和

function fulfilled() {
  return Promise.resolve(1);
}

前者只需要一个 promise tick 就可以解决。

When should I use 'return new Promise(...' in async function?

可能永远不会。参见 How to turn this callback into a promise using async/await?和 What is the benefit of prepending async to a function that returns a promise? .