等待諾言循環

Question

我得到了這個功能：

const upload = (example) => {
    console.log('uploading...');
    return new Promise(function (resolve, reject) {
        resolve & reject
    });
};

我在這里調用上面的函數：

const dirents = await fs.readdirSync(path, {withFileTypes:true});
await Promise.all(dirents.map(async (dirent) => {
    await upload(example).then((response) => {
        console.log('success');
    }, (err) => {
        console.log(err);
    });
});

輸出應為

'uploading' -> 'success' -> 'uploading' ...

但這實際上是

'uploading' -> 'uploading' -> 'success' -> 'success'

我也嘗試了（ for ... of ），但這對我也不起作用。

Answer 1

對於順序承諾，在async函數中使用簡單的循環非常清晰易讀：

 let userIDs = [1, 2, 3]; async function uploadIDS(ids) { for (let id of ids) { let res = await upload(id) console.log("Success:", res) } } const upload = (example) => { console.log('uploading...'); return new Promise(function(resolve, reject) { resolve(example) }); }; uploadIDS(userIDs) 

Answer 2

這是一個將reduce與async/ await使用的現代示例（您可以在此處運行）

let userIDs = [1,2,3];

userIDs.reduce( async (previousPromise, nextID) => {
  await previousPromise;
  return upload(nextID).then((val) => {
    console.log("success", val);
  })
}, Promise.resolve());


const upload = (id) => {
    console.log('uploading...', id);
    return new Promise(function (resolve, reject) {
        resolve(id);
    });
};

Answer 3

**您還可以使用遞歸功能**

 //const dirents = await fs.readdirSync(path, {withFileTypes:true});

    const dirents = [1,2,3]


    const upload = (example) => {
        console.log('uploading...');
        return new Promise(function (resolve, reject) {
            resolve(example)
        });
    };

    function callUpload(dirent, length, count) {

        if(count >= dirents.length){
            return;
        }
        upload(dirent).then(() => {
            count += 1;
            console.log("success")
            callUpload(dirents[count], dirents.length, count)
        })
    }
    callUpload(dirents[0], dirents.length, 0)