在 promise.then 回调后执行操作

Question

我试图在单个 Promise 中封装一些初始化/清理代码。如果执行一些代码，执行 then 然后再执行一些代码，我想要什么。这是我想出的：

function initialize() {
    let callback;
    console.log('intialization');
    const promise = new Promise(resolve => callback = resolve);

    new Promise(async () => {
        await callback();
        await promise;
        console.log('cleanup');
    });

    return promise;
}
initialize().then(() => console.log('execute then'));

这在终端中给出了以下输出：

initialization
execute then
cleanup
- Promise {<fulfilled>: undefined}

到目前为止一切都很好。但是，当我们将回调设为异步时，它就不再起作用了。

initialize().then(
    async () => {
        await new Promise(resolve => {
            setTimeout(
                () => {
                    console.log('execute then');
                    resolve();
                },
                10000
            )
        })
    }
);

给我这个输出：

initialization
cleanup
- Promise {<pending>}
execute then

我希望它看起来像这样：

initialization
- Promise {<pending>}
execute then
cleanup

我该如何解决这个问题？这有可能吗？

Answer 1

您可以接受定义异步操作的回调。然后它可以插入到一个承诺链的中间：

const delayMessage = (message, ms) =>
  new Promise(resolve => setTimeout(() => {
    console.log(message);
    resolve();
  }, ms));

async function somethingAsync() {
  console.log('intialization');
}

function initialize(callback) {
  return somethingAsync()
    .then(callback)
    .then(() => {
      console.log('cleanup');
    });
}
const middleOfProcess = () => delayMessage('execute then', 2000);
initialize(middleOfProcess);

即使中间有多个异步步骤，它也能正常工作，因为您可以简单地将它们链接在一起：

const delayMessage = (message, ms) =>
  new Promise(resolve => setTimeout(() => {
    console.log(message);
    resolve();
  }, ms));

async function somethingAsync() {
  console.log('intialization');
}

function initialize(callback) {
  return somethingAsync()
    .then(callback)
    .then(() => {
      console.log('cleanup');
    });
}

const middleOfProcess = () => delayMessage('execute then1', 2000)
  .then(() => delayMessage('execute then2', 2000))
  .then(() => delayMessage('execute then3', 2000));
initialize(middleOfProcess);

同样可以使用 async/await 语法来完成：

const delayMessage = (message, ms) =>
  new Promise(resolve => setTimeout(() => {
    console.log(message);
    resolve();
  }, ms));

async function somethingAsync() {
  console.log('intialization');
}

async function initialize(callback) {
  await somethingAsync();
  await callback();
  console.log('cleanup');
}

const middleOfProcess = async () => {
  await delayMessage('execute then1', 2000);
  await delayMessage('execute then2', 2000);
  await delayMessage('execute then3', 2000);
};
initialize(middleOfProcess);

在 promise.then 回调后执行操作

Perform an action after a promise.then callback

javascript

promise