Let's talk about how to use third-party open source libraries to implement website crawling function in node

This article will introduce to you how to easily implement the website crawling function with the help of third-party open source libraries in node. I hope it will be helpful to everyone!

nodejsImplementing website crawling function

Introduction to third-party libraries

• request encapsulation of network requests

• cheerio node version of jQuery

• mkdirp creates multiple layers Folder directory

Implementation ideas

• Through request Get the content of the specified url

• ThroughcheerioFind the jump path in the page (remove duplicates)

• ThroughmkdirpCreate directory

• Create a file through fs and write the read content to

• Get Repeat the above steps to the path that is not accessed

Code implementation

const fs = require("fs");
const path = require("path");
const request = require("request");
const cheerio = require("cheerio");
const mkdirp = require("mkdirp");
// 定义入口url
const homeUrl = "https://www.baidu.com";
// 定义set存储已经访问过的路径，避免重复访问
const set = new Set([homeUrl]);
function grab(url) {
  // 校验url规范性
  if (!url) return;
  // 去空格
  url = url.trim();
  // 自动补全url路径
  if (url.endsWith("/")) {
    url += "index.html";
  }
  const chunks = [];
  // url可能存在一些符号或者中文，可以通过encodeURI编码
  request(encodeURI(url))
    .on("error", (e) => {
      // 打印错误信息
      console.log(e);
    })
    .on("data", (chunk) => {
      // 接收响应内容
      chunks.push(chunk);
    })
    .on("end", () => {
      // 将相应内容转换成文本
      const html = Buffer.concat(chunks).toString();
      // 没有获取到内容
      if (!html) return;
      // 解析url
      let { host, origin, pathname } = new URL(url);
      pathname = decodeURI(pathname);
      // 通过cheerio解析html
      const $ = cheerio.load(html);
      // 将路径作为目录
      const dir = path.dirname(pathname);
      // 创建目录
      mkdirp.sync(path.join(__dirname, dir));
      // 往文件写入内容
      fs.writeFile(path.join(__dirname, pathname), html, "utf-8", (err) => {
        // 打印错误信息
        if (err) {
          console.log(err);
          return;
        }
        console.log(`[${url}]保存成功`);
      });
      // 获取到页面中所有a元素
      const aTags = $("a");
      Array.from(aTags).forEach((aTag) => {
        // 获取到a标签中的路径
        const href = $(aTag).attr("href");
        // 此处可以校验href的合法或者控制爬去的网站范围，比如必须都是某个域名下的
        // 排除空标签
        if (!href) return;
        // 排除锚点连接
        if (href.startsWith("#")) return;
        if (href.startsWith("mailto:")) return;
        // 如果不想要保存图片可以过滤掉
        // if (/\.(jpg|jpeg|png|gif|bit)$/.test(href)) return;
        // href必须是入口url域名
        let reg = new RegExp(`^https?:\/\/${host}`);
        if (/^https?:\/\//.test(href) && !reg.test(href)) return;
        // 可以根据情况增加更多逻辑
        let newUrl = "";
        if (/^https?:\/\//.test(href)) {
          // 处理绝对路径
          newUrl = href;
        } else {
          // 处理相对路径
          newUrl = origin + path.join(dir, href);
        }
        // 判断是否访问过
        if (set.has(newUrl)) return;
        if (newUrl.endsWith("/") && set.has(newUrl + "index.html")) return;
        if (newUrl.endsWith("/")) newUrl += "index.html";
        set.add(newUrl);
        grab(newUrl);
      });
    });
}
// 开始抓取
grab(homeUrl);

Summary

The simple web crawler is complete. You can try changing homeUrl to the website you want to crawl.

For more node-related knowledge, please visit: nodejs tutorial! !

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