Building a Web Crawler from Scratch in Node.js
Web crawlers, also known as web spiders or web robots, are programs that browse the Internet in an automated manner. They are used for indexing websites for search engines, gathering specific information from websites, or even for malicious purposes such as scraping content or performing denial of service attacks. In this article, we will learn how to build a simple web crawler from scratch using Node.js.
Step 1: Setting up the project
First, create a new folder for your project and navigate to it in your terminal or command prompt. Then, run the following command to initialize a new Node.js project:
$ npm init -y
This will create a new package.json file with default settings. You can customize it according to your needs.
Step 2: Installing dependencies
Next, we need to install the necessary dependencies for our web crawler. Run the following command to install the axios and cheerio packages:
$ npm install axios cheerio
These packages will allow us to make HTTP requests and parse the HTML content of the websites we want to crawl.
Step 3: Writing the web crawler
Now, create a new JavaScript file (e.g., crawler.js) in your project folder and start writing the code for the web crawler. Below is a simple example of a web crawler that fetches the HTML content of a single web page:
const axios = require('axios');
const cheerio = require('cheerio');
async function crawl(url) {
const response = await axios.get(url);
const $ = cheerio.load(response.data);
// Extract information from the HTML content
}
crawl('https://www.example.com');
Step 4: Running the web crawler
To run the web crawler, simply execute the JavaScript file you created using Node.js:
$ node crawler.js
Make sure to handle errors and implement proper error handling, as well as rate limiting and respecting robots.txt files when crawling websites.
With this simple example, you have learned how to build a basic web crawler from scratch using Node.js. You can further enhance the web crawler by adding features such as following links, storing crawled data in a database, or implementing concurrency for faster crawling. Happy crawling!
Just awesome😁 you not only helped creating a crawler but also taught how to use testcases and code. Thank you soo much 🥳🥳
console.clear() before report would be awesome.
I ran into an issue concerning Jest. Everything passes no issue with just 2 pages concerning sorting for the report. I get an error with any more than 2 pages, stating the output didn't match the expected. I feel this has something to do with the a,b hits function, but cannot for the life of me figure out what. The project works flawlessly in production, it only fails when trying to test with more than 2 pages with Jest. Any ideas on this?
(Edit!)
I just figured it out, for some reason it required me to put the pages in the expected variable in the exact opposite order the input variable pages were ordered and the test passed. A bug from a recent update perhaps? Either way thank you for the knowlege!
@bootdotdev ,for the function getURLfromHTMl test, you are checking both the arrays are equal or not using toEqual< I'm unable to do that donno why, and the other thing is dom.window.querySelectorAll("a") isn't giving the output array, I debugged in my case and found it to be dom.window.querySelectorAll("a") .forEach(linkElement=>{
} this thing, bt still I tried resolving the test error multiple times using toMatch or new Set(actual), but nothing worked………..kindly provide me with a solution….i hope there will be a reply soon……
Ok. It works. It's actually amazing seeing it work (since, from my experience, most code tutorials in you tube, at some point, don't work).
I learnt some Node.js, (mostly Express) to make REST Apps (CRUD). But that was it. A server, some routes, some controllers; Sequelize to post stuff into a Postgres Data Base, and that's it.
This is another level. I just was able to follow the tutorial, but I would be lying if say I understood everything you did. Yes, you import some modules, you install some packages from npm, you tested some functions… yep. And it works, and I don't know how.
How can I learn what you do? I know you are a Backend Developer, but, (at least with Node.js), how did you learnt all that? It's awesome, it really is.
Did he really change a totally clear name of "input" "output" "expected" into "AcTuAl"? I'm pretty sure I have never named anything in my life "Actual" i did do "currentString" etc.
dude jest and jsdom are not compatible..why do u make videoes man ..u diots …the console.log show undefined in mine
Brilliant video and your teaching style is very clear! Is this code available in a GitHub repo or Gist somewhere that I can use for reference at all? Thank you
In sortPages you are creating aHits and bHits but actually dont use them 😛 .. great tutorial thank you.
Cool Project Man !! Learnt a Lot.
47:36 guys let's not DDOS xD
This was great, i learnt more than just crawling the internet… Am experimenting with TDD with Jest. thanks a banch.
Subscribed ! You're other videos seem interesting, I'm checking em out soon. Nice content 👍
Simply amazing.
Nice video, clear sound, more information and very helpful
Thank you so much for this working hard
We need more of these projects of nodejs
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