在異步函數中返回承諾-什么是更優雅/更好的實踐解決方案？

Question

我對async / await相當陌生，盡管以下代碼似乎可以正常工作，但我認為必須有一種更為優雅/最佳實踐的方式來編寫此函數：

    /**
     * 
     * @param {string} email user email address
     * @description validates project exists and project owner is userId.
     * @returns {Promise} resolves userId if found otherwise null
     */
    async getUserFirstAndLastName (userId) {
        var userName;
        return new Promise(function(resolve, reject){
            var params = {
                UserPoolId: process.env.userPoolId, /* required */
                AttributesToGet: [
                'given_name',
                'family_name'
                /* more items */
                ],
                Filter: `sub = \"${userId}\"`
            };
            console.log("UserUtils DDB Get User First and Last Name:" + JSON.stringify(params, null,'  '));
            cognitoidentityserviceprovider.listUsers(params, function(err, data) {
                if(err){ // an error occurred
                    console.log(err, err.stack);
                    reject(err); // throw error
                }
                else { // successful response
                    console.log("Data: " + JSON.stringify(data, null,'  '));
                    if(data.Users.length){
                        userName = data.Users[0].Attributes[0].Value + " "; // First Name
                        userName += data.Users[0].Attributes[1].Value; // Last Name
                        resolve(userName); //return
                    }
                    else {
                        resolve(null); // no user found that matches email
                    }
                }
            });
        });
    }

尋求指導...

Answer 1

您的代碼問題確實似乎在以下方面：

cognitoidentityserviceprovider.listUsers(params, function(err, data) {
    ...
});

這是處理異步代碼的舊回調樣式方法 。

您想要編寫代碼的真正方法是，不是讓listUsers函數接受回調，而是返回一個promise。 然后，您可以通過以下方式編寫代碼：

async getUserFirstAndLastName (userId) {
        const params = {
            UserPoolId: process.env.userPoolId, /* required */
            AttributesToGet: [
            'given_name',
            'family_name'
            /* more items */
            ],
            Filter: `sub = \"${userId}\"`
        };

        try {
            const data = await cognitoidentityserviceprovider.listUsers(params);
            if(data.Users.length){
                let userName = data.Users[0].Attributes[0].Value + " "; // First Name
                userName += data.Users[0].Attributes[1].Value; // Last Name
                return userName; 
            }
            else {
                return null; // no user found that matches email
            }
        }catch(err) {
            throw err; 
        });
    });
}

假設您不能直接重寫該listUsers函數，則可以編寫一個將其轉換為返回promise的函數的函數，如下所示：

function convertCallbackFnToAsyncFn(fn) {
    //Note that we are returning a function
    return (...args) => new Promise(function(resolve, reject){
        fn(...args, (err, data) => {
             if (err) {
                reject(err); 
             }
             else {
               resolve(data); 
             }
        }); 
    }); 
}

並將其與上述解決方案配合：

        try {
            //I'm just naming it newFunction here to be really clear about what we're doing
            const newFunction = convertCallbackFnToAsyncFn(cognitoidentityserviceprovider.listUsers);
            const data = await newFunction(params);
            ....

請注意，我在答案中使用了一些ES6傳播/休息和粗箭頭語法。