javascript - 将 promise 与 promise all 链接起来会导致意外的执行顺序

Question

为什么下面的代码在 1, 2, 3 之前打印 baz, done？

const bar = () => Promise.resolve([1, 2, 3]);
const cat = e => {
  console.log(e);
  return Promise.resolve(e);
};
const foo = () =>
  bar()
    .then(arr => Promise.all(arr.map(e => cat(e))))
    .then(console.log("baz"));

foo().then(console.log("done"));

Answer 1

您正在立即执行 console.log() 而不是将其传递给 .then() 中的回调函数。这将做到:

const bar = () => Promise.resolve([1, 2, 3]);

const cat = e => {
  console.log(e);
  return Promise.resolve(e);
};

const foo = () =>
  bar()
    .then(arr => Promise.all(arr.map(e => cat(e))))
    .then(() => console.log("baz"));
    
foo().then(() => console.log("done"));