在 promise.then 回調后執行一個動作

Question

我正在嘗試將一些初始化/清理代碼封裝在一個 Promise 中。我想要的是執行一些代碼，然后執行然后再執行一些代碼。 這就是我想出的：

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'));

這在終端中給了我以下 output：

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

到目前為止一切都很好。 但是，當我們使回調異步時，它就不再起作用了。

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

給我這個 output：

initialization
cleanup
- Promise {<pending>}
execute then

我本來希望它看起來像這樣：

initialization
- Promise {<pending>}
execute then
cleanup

我怎樣才能解決這個問題？ 這有可能嗎？

Answer 1

您可以接受定義異步操作的回調。 然后它可以插入到 promise 鏈的中間：

 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);

即使中間有多個異步步驟，它也能正常工作，因為你可以簡單地將它們鏈接在一起：

 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);

同樣可以使用 async/await 語法來完成：

 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);