Node基础

2018-03-12  本文已影响0人  Love小六六

什么是Nodejs

Node模块分类

模块的流程

Node.js API

HTTP知识

使用Apache ab
ab -n1000 -c10 https:www.imooc.com/
// -n 1000 总请求数是1000个
// -c10 并发数为10 

/**
 * 一个初级爬虫Demo
 */
var https = require('https');
var cheerio = require('cheerio');
var url = 'https://www.imooc.com/learn/348';


// 请求url地址,获取页面html
https.get(url,function (res) {
    var html = '';
    res.on('data',function(data){
        html += data;
    });
    res.on('end',function () {
        var courseData = filterCharpter(html);
        printChapter(courseData);
    });
    res.on('error',function () {
        console.log('系统异常');
    })
})

// 获取页面章节的函数
function filterCharpter (html) {
    var $ = cheerio.load(html);
    var chapters =$('.chapter');
    var courseData = [];
    chapters.each(function (value) {
        var chapter = $(this);
        var chapterTitle = chapter.find('strong').text().trim().split('\n')[0];
        var videos = chapter.find('.video').children('li');
        chapter = {
            chapterTitle : chapterTitle,
            videos:[]
        }
        videos.each(function(val){
            var video = $(this).find('a').text().trim();
            var videoName = video.split('\n')[0];
            var videoTime = video.split('\n')[1].trim();
            chapter.videos.push({name:videoName,time:videoTime});

        });
        courseData.push(chapter);
    });
   return courseData;
}
// 格式化打印页面
function printChapter (courseData) {
    courseData.forEach(function (val) {
        var chapterTitle = val.chapterTitle;
        console.log('章节标题:'+chapterTitle+'\n');
        val.videos.forEach(function (value) {
            console.log('  '+value.name+'时长:'+value.time+'\n');
        })
    })
}

promise

针对异步场景的解决方案

promiseObj.then(onResolved,onRejected);
onResolved = function(value){
    return promiseObj2;//返回一个promise对象
}
onRejected = function(err){}

var https = require('https');
var cheerio = require('cheerio');

var baseUrl = 'https://www.imooc.com/learn/'
var videosArray = [728,637,348,259,197,134,75];
videosArray = videosArray.map(item => baseUrl+item);
// 创建promise
function getPageAsync(url){
    return new Promise(function(resolve,rejecte){
        // 请求url地址,获取页面html
        https.get(url,function (res) {
            var html = '';
            res.on('data',function(data){
                html += data;
            });
            res.on('end',function () {
                resolve(html);
            });
            res.on('error',function (error) {
                rejecte(error);
            })
        })
    })
}

// 获取页面章节的函数
function filterCharpter (html) {
    var $ = cheerio.load(html);
    var title  = $('.course-infos h2').text().trim();
    var page = {
        title:title,
        courseData:[]
    }
    var chapters =$('.chapter');
    var courseData = [];
    chapters.each(function (value) {
        var chapter = $(this);
        var chapterTitle = chapter.find('strong').text().trim().split('\n')[0];
        var videos = chapter.find('.video').children('li');
        chapter = {
            chapterTitle : chapterTitle,
            videos:[]
        }
        videos.each(function(val){
            var video = $(this).find('a').text().trim();
            var videoName = video.split('\n')[0];
            var videoTime = video.split('\n')[1].trim();
            chapter.videos.push({name:videoName,time:videoTime});

        });
        courseData.push(chapter);
    });
    page.courseData = courseData;
    return page;
}

// 打印章节内容
function printCourseData (coursesData) {
    coursesData.forEach(function(item){
        console.log('课程名:'+item.title+'\n');
        item.courseData.forEach(function(val){
            var chapterTitle = val.chapterTitle;
            console.log('   '+chapterTitle+'\n');
            val.videos.forEach(function (value) {
                console.log('      '+value.name+'时长:'+value.time+'\n');
            })
        })
        console.log('\n');
    })
}
// 所有页面的promise数组
var pagesPromiseArray = [];
videosArray.forEach(function(val){
    pagesPromiseArray.push(getPageAsync(val));
})

//promise.all方法
Promise
    .all(pagesPromiseArray)
    .then(function (pages) {
        var coursesData = [];
        pages.forEach(function(html){
            var courses = filterCharpter(html)
            coursesData.push(courses)
        })
        printCourseData(coursesData);
    })
    .catch (function (e) {
        console.log('程序异常');
    })

Node API

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