将异步函数返回值分配给 Node.JS 中的变量

Question

我在下面有一个函数可以从 DynamoDB 中获取数据，然后 returns 根据条件评估判断真假。此功能将用于进行简单检查并确定用户的海拔高度以进行数据访问等等。

我怎样才能让这个函数做类似的事情：

var auth = aliasHasRole('foo','bar')
console.log(auth) // prints value passed down by aliasHasRole().

我想我必须将其声明为 async 并在返回之前添加 await 但没有运气，然后 aliashHasRole('foo','bar').then( (x) => { auth = x})，但它 returns undefined.

完整代码如下：

var AWS = require('aws-sdk');
AWS.config.update({
    region: 'us-west-2',
    accessKeyId: "xxx",
    secretAccessKey: "xxx",
});
const docClient = new AWS.DynamoDB.DocumentClient();


function aliasHasRole(an_alias, a_role) {
    const params = {
        TableName: 'xxx',
        KeyConditionExpression: '#alias= :alias AND #Role= :Role',
        ExpressionAttributeNames: {
            '#alias': 'alias',
            '#Role': 'Role'
        },
        ExpressionAttributeValues: {
            ':alias': an_alias,
            ':Role': a_role,
        }
    };

    docClient.query(params).promise()
        .then(
            (data) => {
                //this line below returns true or false, how can I get I pass this value so I can return it from the aliasHasRole as true or false?
                console.log(data.Items.length > 0 && data.Items[0].alias === an_alias && data.Items[0].Role === a_role ? true : false);
                return data.Items.length > 0 && data.Items[0].alias === an_alias && data.Items[0].Role === a_role ? true : false;
            })
        .catch((err) => {
            console.log(err)
        })
};

var auth;
aliasHasRole("xxx","TeamManager");//should return true or false just like it logs it to the console.
//Do something to assign functions value to var auth.
console.log(auth) //print value passed by function...

//How can I assign this value to a variable? as in var auth = aliasHasTole('foo','bar') // auth is now true or false.

Answer 1

你没有使用 async/await 关键字 right.Modify 你的函数像这样试试。

var AWS = require('aws-sdk');
AWS.config.update({
    region: 'us-west-2',
    accessKeyId: "xxx",
    secretAccessKey: "xxx",
});
const docClient = new AWS.DynamoDB.DocumentClient();

// you can use async and await like this
let aliasHasRole = async function (an_alias, a_role) {

    try {
        const params = {
            TableName: 'xxx',
            KeyConditionExpression: '#alias= :alias AND #Role= :Role',
            ExpressionAttributeNames: {
                '#alias': 'alias',
                '#Role': 'Role'
            },
            ExpressionAttributeValues: {
                ':alias': an_alias,
                ':Role': a_role,
            }
        };

        // this will resolve the value 
        let data = await docClient.query(params).promise()
        return data.Items.length > 0 && data.Items[0].alias === an_alias && data.Items[0].Role === a_role ? true : false;
    }
    catch (err) {
        //this is equivalent .catch statement
        console.log(err)
    }
};
// This has to be self executing function in case of async await
(async () => {
    var auth = await aliasHasRole("xxx", "TeamManager");
    // This will print the value of auth which will be passed from the aliasHasRole ie. True or False
    console.log(auth) //print value passed by function aliasHasRole...
})()

你也可以在没有 async/await

的情况下使用它


var AWS = require('aws-sdk');
AWS.config.update({
    region: 'us-west-2',
    accessKeyId: "xxx",
    secretAccessKey: "xxx",
});
const docClient = new AWS.DynamoDB.DocumentClient();

// you can use async and await like this
function aliasHasRole(an_alias, a_role) {

    const params = {
        TableName: 'xxx',
        KeyConditionExpression: '#alias= :alias AND #Role= :Role',
        ExpressionAttributeNames: {
            '#alias': 'alias',
            '#Role': 'Role'
        },
        ExpressionAttributeValues: {
            ':alias': an_alias,
            ':Role': a_role,
        }
    };

    // Return is the main part. The error was that you are not using the return key word with Promise that's why it was not working
    return docClient
        .query(params)
        .promise()
        .then(data => data.Items.length > 0 && data.Items[0].alias === an_alias && data.Items[0].Role === a_role ? true : false)
        .catch(error => {
            // You can handle the error here
            console.log(error)
        })
};


aliasHasRole("xxx", "TeamManager").then(auth => {
    // This will print the value of auth which will be passed from the aliasHasRole ie. True or False
    //print value passed by function...
    console.log(auth)
})

将异步函数返回值分配给 Node.JS 中的变量

Assign Async function returned value to a variable in Node.JS

asynchronous

node.js

async-await

amazon-dynamodb

aws-sdk-nodejs