Question

我有一个promise函数，该函数会进行两次请求调用，并在第二次调用完成后解决。第二个解析调用也取决于第一个调用中的数据。但是在then函数中，变量返回值我为null。任何帮助将不胜感激。

编辑：secResp.body具有正确的数据，它不是null

const express = require('express');
const request = require('request');
const app = express();
const port = process.env.PORT || 5000;

// console.log that your server is up and running
app.listen(port, () => console.log(`Listening on port ${port}`));

app.get('/api/currentMatch/:name', function(req, res, next){
    getPlayersInMatch(req.params.name).then(function(participants){
        //this is null
        console.log(participants);
    }).catch(function (err) {
     console.log(err);
    });
})

function getPlayersInMatch(name){
    return new Promise(function(resolve, reject){
        request.get({
            url: api_url
        }, function(firstErr, firstResp, body){
            if(firstResp.StatusCode != 200){
                reject(firstErr);
            }
            var accountId = JSON.parse(firstResp.body).id;
            request.get({
                url: api_url2 + 'accountId=' + accountId
            }, function(secErr, secResp, body){
                if(secResp.StatusCode != 200){
                    reject(secErr);
                }
                //this is not null, this is an array
                var participants = JSON.parse(secResp.body).participants;
                resolve(participants);
            });
        });
    });
}

Answer 1

我将您的代码重写为request-promise。我发现您的代码的主要问题是它太复杂了。简化事情可以更轻松地发现您做错了什么。

const rp = require('request-promise')
const app = express();
const port = process.env.PORT || 5000;

// console.log that your server is up and running
app.listen(port, () => console.log(`Listening on port ${port}`));

app.get('/api/currentMatch/:name', function(req, res, next){
    getPlayersInMatch(req.params.name)
        .then(console.log)
        .catch(console.error)
})

const getPlayersInMatch = async name => {
    const id = await rp(api_url)
        .then(res => JSON.parse(res.body).id)

    const participants = await rp(api_url2 + 'accountId=' + accountId)
        .then(res => JSON.parse(res.body).participants)

    return { id, participants }
}

Answer 2

        <p>Enter in how many fingers (between 0 and 5) you are holding up: </p>

        <p>
            <input id="fingersInput" type="text">
            <button id="fingersSubmit">Guess!</button>
        </p>

        <div id="fingers-game-v2"></div>

        <p id="computer-guess-results"></p>

        <script type="text/javascript">

            var numberOfFingers = document.getElementById("fingersInput").value;

            var fingersText = "";

            var correctGuesses = 0;  

            document.getElementById("fingersSubmit").onclick = function ()
                {
                i = 0;

                while (i < 5)
                    {
                        var computerGuess = Math.floor((Math.random()*5)+1);

                        fingersText += "<p>" + computerGuess + "</p>";

                        if (computerGuess == numberOfFingers)
                            {
                                var correctGuesses = correctGuesses + 1;
                            }

                        i++;
                    }

                document.getElementById("fingers-game-v2").innerHTML = fingersText;

                document.getElementById("computer-guess-results").innerHTML = "<h3>" + "Number of times the computer guessed correctly: " + "</h3>" + correctGuesses; 
                }

尝试一下。

一个，应该返回请求结果或对象。第二，您应该使用async await，因为它不等待异步回调中的数据请求。

Answer 3

在您的代码中，很难找出哪个步骤出错。

我认为最好将请求模块包装为：

/**
 * Mapping knowing error_code
 * @param {Number} error_code 
 * @param {String} msg 
 */
function error_def(error_code, msg) {
    let status, message;
    switch(error_code){
        case 400:
        case 401:
        case 402:
        case 403:            
        case 1000:
        case 1001:
        case 1002:
        case 1003:
        case 1005:
            status = error_code;
            message = msg;
            break;
        default:
            status =  2000;
            message = 'Undefined Error'
    }
    return {status: status, msg: message};
}

/**
 * Generate error message
 * @param {String} tag
 * @param {Number} error_code
 * @param {String} msg
 */
function gen_error_func(tag = null) {    
    return function(error_code, msg = null) {
        return {tag: tag, error_message: error_def(error_code, msg)}
    }
}

/**
 * Wrap the request and return interesting keys
 * @param {String} tag 
 * @param {Object} req_opt 
 * @param {Array} interesting_resp
 * @return {Object}
 */

function req_wrap(tag = null, req_opt, interesting_resp = null){
    return new Promise((resolve, reject) => {
        let gen_error = gen_error_func(tag)

        if (!req_opt.url) {
            reject(gen_error(1000, 'missing url'));
        }

        let option = {
            url: req_opt.url,
            method: (req_opt.method)? req_opt.method: 'GET',
        }

        request(option, function(error, response, body) {
            if(error) {
                reject(gen_error(1001, error));
                return;
            }

            if (!response) {
                reject(gen_error(1005, 'response is undefine, maybe wrong url!'))
                return;
            }

            if (response.statusCode >= 400) {
                //http level error
                reject(gen_error(response.statusCode, body));
            }else {
                let result = {};
                let body_json;
                try {
                    body_json = JSON.parse(body);
                }catch(e) {
                    reject(gen_error(1002, `Unknow response: ${body}`))
                }
                if (interesting_resp) {
                    interesting_resp.map(key => {
                        if (body_json[key] == undefined) {
                            reject(gen_error(1003, `In ${body_json}, undefined ${key}`))
                            return;
                        }
                        result[key] = body_json[key];
                    })
                }else {
                    result = body_json;
                }
                resolve(result);
            }
        })
    })
}

req_wrap：
- 参数
  - 标签：显示您定义的请求，例如：“首次连接”
  - req_opt ：请求选项
  - interesting_resp ：您感兴趣的键

注意：在req_wrap中，如果无法在 interesting_resp 中找到响应键（未定义或为null），该函数将拒绝。有必要检查您要求的服务器规格！

您可以重写代码：

function getPlayersInMatch(name){
    return new Promise(function(resolve, reject){
        req_wrap('first_conn', {url: api_url}, ['id']).then(result => {            
            req_wrap('second_conn', {url: api_url2 + 'accountId=' + result.id}, ['participants']).then(result => {
                resolve(result.participants)
            }).catch(error => {
                reject(error)
            })
        }).catch(error => {
            reject(error)
        })
    });
}

现在更清楚地检查哪一步是错误的。

Nodejs Promise无法解析/未返回数据

3 个答案: