使用http.get node.js的Promise

Question

我正在做nodechool练习,

此问题与上一个问题(HTTP COLLECT)相同,因为您需要使用http.get().但是,这次您将获得三个URL作为前三个命令行参数.

您必须收集每个URL提供给您的完整内容,并将其打印到控制台(stdout).您不需要打印长度,只需将数据打印为String; 每个网址一行.问题是您必须按照与作为命令行参数提供的URL相同的顺序打印它们.

换句话说,我要注册3个http.get请求,并按顺序打印从中收到的数据.

我试图用promises做另外一个get请求不会被调用直到第一个没有结束.

我的代码看起来像这样

var http=require("http");
var collect=[];
var dat=[];
for( var i = 2 ; i < process.argv.length;i++){
    collect.push(process.argv[i]);
}

function chainIt(array,callback){
    return array.reduce(function(promise,item){
        return promise.then(function(){
            return callback(item)
        })
    },Promise.resolve())
}



function getIt(item){
    return http.get(item,function(response){
        response.on("data",function(data){
                dat.push(data);
        })

    })
}


chainIt(collett,function(item){
    return getIt(item)
    })
}).then(function(){
    collect.forEach(function(x){
            console.log(x);
    })

})

但我实际上没有打印数据=我没有通过练习.

我没有看到任何错误,但我只是从promises和node开始.哪里出错了？

Answer 1

对于教育目的,我最近写了一个包装http,并https使用本机模块Promise秒.也就是说,我建议使用一个库,这样的request; 这使事情更简单,具有单元测试覆盖率,由开源社区维护.此外,我的包装器与响应块进行了一个天真的字符串连接,我不相信这是建立响应主体的最高效方式.

仅供参考:这需要Node.js 4或更高版本,尽管Node 0.xx中的方法几乎相同

'use strict';

const http = require('http');
const url = require('url');

module.exports = {
    get(url) {
        return this._makeRequest('GET', url);
    },

    _makeRequest(method, urlString, options) {

        // create a new Promise
        return new Promise((resolve, reject) => {

            /* Node's URL library allows us to create a
             * URL object from our request string, so we can build
             * our request for http.get */
            const parsedUrl = url.parse(urlString);

            const requestOptions = this._createOptions(method, parsedUrl);
            const request = http.get(requestOptions, res => this._onResponse(res, resolve, reject));

            /* if there's an error, then reject the Promise
             * (can be handled with Promise.prototype.catch) */
            request.on('error', reject);

            request.end();
        });
    },

    // the options that are required by http.get
    _createOptions(method, url) {
        return  requestOptions = {
            hostname: url.hostname,
            path: url.path,
            port: url.port,
            method
        };
    },

    /* once http.get returns a response, build it and 
     * resolve or reject the Promise */
    _onResponse(response, resolve, reject) {
        const hasResponseFailed = response.status >= 400;
        var responseBody = '';

        if (hasResponseFailed) {
            reject(`Request to ${response.url} failed with HTTP ${response.status}`);
        }

        /* the response stream's (an instance of Stream) current data. See:
         * https://nodejs.org/api/stream.html#stream_event_data */
        response.on('data', chunk => responseBody += chunk.toString());

        // once all the data has been read, resolve the Promise 
        response.on('end', () => resolve(responseBody));
    }
};

编辑:我只是意识到你是新手Promise.以下是如何使用此包装器的示例:

'use strict';

const httpService = require('./httpService'); // the above wrapper

// get one URL
httpService.get('https://ron-swanson-quotes.herokuapp.com/v2/quotes').then(function gotData(data) {
    console.log(data);
});

// get multiple URLs
const urls = [
    'https://ron-swanson-quotes.herokuapp.com/v2/quotes',
    'http://api.icndb.com/jokes/random'
];

/* map the URLs to Promises. This will actually start the
 * requests, but Promise.prototype.then is always called,
 * even if the operation has resolved */
const promises = urls.map(url => httpService.get(url));

Promise.all(promises).then(function gotData(responses) {
    /* responses is an array containing the result of each
     * Promise. This is ordered by the order of the URLs in the
     * urls array */

    const swansonQuote = responses[0];
    const chuckNorrisQuote = responses[1];

    console.log(swansonQuote);
    console.log(chuckNorrisQuote);
});

Answer 2

其中一种方法是使用“Q”库。

首先创建将命中 URL 并返回 Promise 的函数

var Q = require('q);
function getIt(item){
 return http.get(item,function(response){

       return Q.resolve(response); // Return response
         OR
       return Q.resolve(error);    // Return error

     })
  })
}



var urls = ['url1','url2','url3']; // list of urls

Q.spread(urls.map(getIt))
 .then(function(res1,res2,res3){ 

    // res1 is response for url1 and on
    //Once all calls are finished you will get results here
 });