Puppeteer爬取网页数据

动机

但愿能够从各大技术论坛抓取本身感兴趣的问题。

技术

• puppeteer
• dotenv

详细设计

• 核心功能：使用puppeteer仿真用户在浏览器上的行为，操做DOM获取数据
• 快速启动：使用dotenv将不一样论坛之间的差别项（如元素的选择器等）写入环境变量，而后在package.json文件里配置启动命令，快速启动

1. 目录结构

|-- env
     |-- csdn.env
     |-- segmentfault.env
|-- index.js
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2. 代码设计

代码逻辑特别简单，主要流程以下：

1. 打开浏览器
2. 建立一个新的页面
3. 跳转到目标网站
4. 获取数据
5. 将数据打印到控制台（或者写入到数据库）
6. 关闭浏览器

由于puppeteer很容易仿真用户在浏览器上的行为，因此DEMO的核心在于如何获取数据，或者说如何实现get_news方法。

const puppeteer = require("puppeteer");
   
(async () => {
 // 1. Open browser
 const browser = await puppeteer.launch({});
  // 2. Create a new page
 const page = await browser.newPage();
  // 3. Go to the target website
  await page.goto(url, { waitUntil: "networkidle2" });
  // 4. Get data
  let data = await page.evaluate(get_news);
  // 5. Print out the data in the console
  console.log(data);
  // 6. Close browser
  await browser.close();
})();
   
// Getting news
function get_news() {
    // To do something to get news
}
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以CSDN为例，以下图所示，在网页里咱们能够很容易的经过原生的DOM操做document.querySelector(selector)或者jQuery的DOM操做$(selector)来找到页面上的元素，从而获取页面信息。在puppeteer的page.evaluate方法同时支持原生的DOM操做和jQuery的DOM操做，所以咱们获取页面数据就会变得很容易。具体代码以下所示。

function get_news() {
  let result = [];
  let titles = $(".forums_title");
  let dates = $(".forums_author em");
  titles.map((i, title) => {
    result.push({
      title: title.text,
      link: title.href,
      date: dates[i].textContent
    });
  });
  return result;
}
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如今运行代码能够在控制台中打印出抓取到的网页数据，以下图所示。你一样能够将数据写入到数据库。

3. 更多细节

代码里还有不少的细节实现，由于都有详细的注释我就不一一展开了，感兴趣的小伙伴能够阅读后面的代码。主要包括的技术细节以下：

• 怎么经过dotenv配置环境变量
• 怎么在puppeteer的page.evaluate里用console调试
• 问题有效时间，关键字的检查
• 怎么在package.json文件里配置快速启动的命令

参考

• Puppeteer API
• puppeteer-examples

后记

我在前端上仍是个小白，代码质量可能不高，若是有什么问题但愿你们在评论区里及时指出，帮助小白成长，感激涕零！！！

完整代码

1. index.js

const puppeteer = require("puppeteer");
const {
  resolve
} = require("path");
 
(async(path_name, start_time) = >{
  // 1. Analytical path of environmental variables
  let dotenvPath = resolve(__dirname, "env", path_name);
  require("dotenv").config({
    path: dotenvPath
  });
 
  // 2. Open browser
  const browser = await puppeteer.launch({});
 
  // 3. Create a new page
  const page = await browser.newPage();
 
  // Catch headless navigator's console event
  page.on("console", msg = >{
    for (let i = 0; i < msg.args().length; ++i) {
      console.log(`$ {i}: $ {msg.args()[i]}`);
    }
  });
 
  // 4. Getting env variables
  let tags = JSON.parse(process.env.TAGS);
  let titles = process.env.SELECTOR_TITLES;
  let dates = process.env.SELECTOR_DATES;
  let keywords = JSON.parse(process.env.KEYWORDS);
  let time_interval = process.env.TIME_INTERVAL;
  let para = { path_name, start_time, time_interval, titles, dates, keywords};
 
  // Get page url based on label and page index
  const get_news_url = (tag, pageIndex) = >process.env.LIST_URL.replace("{tag}", tag).replace("{pageIndex}", pageIndex);
 
  // 5. Traverse through all tags to get data
  await Promise.all(tags.map(async tag => {
    let i = 0;
    while (true) {
      // 1) Go to the specified page
      await page.goto(get_news_url(tag, ++i), { waitUntil: "networkidle2" });
      // 2) Get data by function get_news
      let _titles = await page.evaluate(get_news, para);
      // 3) Stop the loop if it can't find the required data
      if (_titles.length === 0) break;
      // 4) Output captured data in console
      console.log(i, get_news_url(tag, i));
      console.log(_titles);
    }
  }));
 
  // 6. Close browser
  await browser.close();
})(process.env.PATH_NAME, process.env.START_TIME);
 
// Getting news
async
function get_news(para) {
  // Get release time of issue
  const get_release_time = dom => {
    if (path_name === "csdn.env") return dom.textContent;
    if (path_name === "segmentfault.env") return new Date(dom.dataset.created * 1000);
  }
 
  // Check whether the issue release time is within the valid time interval
  const validate_time = (time, start_time) => {
    let time_diff = (new Date(time)) - (new Date(start_time));
    return (time_diff > 0) && (time_diff < time_interval);
  }
 
  // Check to see if the keyword is included
  const validate_keyword = (keywords, title) => !!keywords.find(keyword = >(new RegExp(keyword)).test(title))
 
  // 1. Waiting for callback data
  let { path_name, start_time, time_interval, titles, dates, keywords } = await Promise.resolve(para);
 
  // 2. Traverse the page data to find the required data
  let result = [];
  $(titles).map((i, title) => {
    // 1) Verify that the data is valid in time
    let check_time = validate_time(get_release_time($(dates)[i]), start_time);
    if (!check_time) return;
    // 2) Verify that the data contains the specified keywords
    let check_keyword = validate_keyword(keywords, a.text);
    if (!check_keyword) return;
    result.push({
      title: title.text,
      link: title.href,
      date: get_release_time($(dates)[i]).toString()
    });
  });
  return result;
}
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2. csdn.env

LIST_URL=https://bbs.csdn.net/forums/{tag}?page={pageIndex}
TAGS=["CSharp","DotNET"]
KEYWORDS=[".net","C#","c#"]
SELECTOR_TITLES=.forums_topic .forums_title
SELECTOR_DATES=.forums_author em
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3. segmentfault.env

LIST_URL=https://segmentfault.com/questions/unanswered?page={pageIndex}
TAGS=[""]
KEYWORDS=["js","mysql","vue","html","javascript"]
SELECTOR_TITLES=.title a
SELECTOR_DATES=.askDate
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4. package.json

{
  "name": "fetch-question",
  "version": "1.0.0",
  "description": "fetch questions from internet",
  "main": "index.js",
  "dependencies": {
  "cross-env": "^5.2.0",
  "dotenv": "^7.0.0",
  "puppeteer": "^1.13.0"
},
  "devDependencies": {},
  "scripts": {
    "csdn:list": "cross-env PATH_NAME=csdn.env START_TIME=2019/3/18 TIME_INTERVAL=172800000 node index.js",
    "segmentfault:list": "cross-env PATH_NAME=segmentfault.env START_TIME=2019/3/18 TIME_INTERVAL=172800000 node index.js",
},
  "author": "linli",
  "license": "ISC"
}
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