How to write a crawler in nodejs

In today’s digital era, the amount of data on the Internet is growing exponentially. Therefore, crawlers are becoming increasingly important. More and more people are using crawler technology to get the data they need. Among the most popular programming languages ​​in the world, Node.js is becoming one of the most popular development languages ​​for crawlers due to its efficient, lightweight and fast features. So, how to write a crawler in Node.js?

Introduction

Before we start to introduce how to write a crawler in Node.js, let’s first understand what a crawler is. Simply put, a crawler is a technical method that automatically obtains Internet information through programs. The crawler collects the required data from the target website by automating tests, accessing server endpoints, or parsing HTML directly. The main purposes of using crawlers include crawling data on websites, automating testing, and comprehensively measuring competitors and SEO.

Node.js

Node.js is a cross-platform, open source JavaScript runtime environment for building efficient, scalable, event-driven applications. Due to its extremely high performance and reliability, Node.js has become one of the best choices for building web applications. Node.js is also an excellent crawler development tool with excellent asynchronous programming capabilities that can efficiently collect data in the shortest possible time.

Implementing a crawler

Let’s take a look at how to use Node.js to implement a simple crawler. The website we will crawl is the content of Wikipedia China. The following are the tools and steps we will use:

1. Request: A simple and powerful http request tool that can use very few Conveniently make HTTP requests in just a few lines of code.
2. Cheerio: A jQuery-like parsing tool that allows you to parse html and xml documents with Node.js.

This is our Node.js code:

const request = require('request');
const cheerio = require('cheerio');
const url = 'https://zh.wikipedia.org/wiki/%E4%B8%AD%E5%9B%BD';

request(url, function(error, response, html) {
    if (!error) {
        var $ = cheerio.load(html);

        // 获取页面标题
        var pageTitle = $('title').text();
        console.log(pageTitle);

        // 爬取链接
        var links = $('a');
        $(links).each(function(i, link){
            var fullLink = $(link).attr('href');
            console.log(fullLink);
        });
    }
});

We obtain the HTML document of the page through the Request module, and then parse the document through the Cheerio module to extract the page title and link information.

Summary

Writing a crawler with Node.js is a relatively simple task, but you also need to pay attention to some key issues, such as the frequency of obtaining data, data storage, and how to maintain the crawler program. I hope this article can help you better understand how to use Node.js to write crawlers, get more data information from it, and improve your data collection and data analysis capabilities.

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