A brief introduction to Node.js to implement crawlers

A brief introduction to Node.js to implement crawlers

Node.js is a JavaScript runtime environment that implements server-side programming with JavaScript as the control language, and can be used to write scripts that implement crawler functions.

The realization principle of reptiles

A crawler is a tool that automatically extracts data from web pages, such as extracting user names, comments, and other data from web pages.

The realization principle of the crawler is to use Node.js to send an http request, then parse the html document, and extract the required data from the page according to the specified xpath rules or regular expressions.

Using Node.js to Implement a Crawler

To use Node.js to implement the crawler function, you first need to install the Node.js environment, and then you need to choose a module that implements the crawler function, commonly used are cheerio, request, superagentand so on.

use cheerio

cheerioIt is the most commonly used tool to implement crawlers in the Node.js environment. It is a server-side implementation of jQuery, which can directly extract data from the page using jQuery syntax.

First install cheerio:

npm install cheerio

Then use cheerio to make an http request, fetch the html document, and use jQuery syntax to extract the required data:

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

request('http://example.com', function (error, response, body) {
    
    
  if (!error && response.statusCode == 200) {
    
    
    var $ = cheerio.load(body);
    var title = $('title').text();  // 获取title
    var comments = $('.comment').text();  // 获取评论
    //...
  }
});

use request

requestIt is a tool used to issue http requests in the Node.js environment, and can directly use regular expressions or xpath rules to extract data from html documents.

First install request:

npm install request

Then use request to make an http request, get the html document, and use regular expressions or xpath rules to extract the required data:

var request = require('request');

request('http://example.com', function (error, response, body) {
    
    
  if (!error && response.statusCode == 200) {
    
    
    var title = body.match(/<title>(.*?)<\/title>/);  // 使用正则表达式提取title
    var comments = request('http://example.com/comments').xpath('//div[@class="comment"]');  // 使用xpath提取评论
    //...
  }
});

in conclusion

Node.js can easily realize the crawler function, and the crawler function can be easily realized by using ready-made modules, such as cheerio, request, superagent, etc.