Peterson Oaikhenah
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A practical guide to web scraping in Nodejs

A practical guide to web scraping in Nodejs

Peterson Oaikhenah's photo
Peterson Oaikhenah
ยทAug 16, 2020ยท

7 min read

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Data has never been so needed and openly accessible as it is today. Why?

This is because Accurate and up-to-date information drives modern technology, businesses, major decisions, strategic approaches to problems, access to resources around you e.t.c

The need to harvest such data, openly available on the web in an automated fashion, prompts web scraping techniques.

What is web scraping?

In simple terms it's a technique employed to extract specific amounts of data from websites whereby the data is extracted and saved to a local file in a computer or to a database. So instead of manually copying the data from websites, the Web Scraping tool will perform the same task within a fraction of the time. web scraping.png Photo by WebHarvy

Let's demo a simple data harvest in Nodejs, Tools needed:

  • Puppeteer - it's a Node library which provides a high-level API to control Chrome. its also a headless browser and a pretty fast tool.
  • Nodejs - Node.jsยฎ is a JavaScript runtime built on Chrome's V8 JavaScript engine, for server side applications.

    Getting started

    Installation.

To use Puppeteer in your project, run:

npm i puppeteer
# or "yarn add puppeteer"

Nodejs server setup.

Let's spin up a Nodejs sever to respond to our web scraper API call,

const express = require('express');
const app = express();
const cors = require('cors')
const dotenv = require('dotenv');
dotenv.config()

// scraper model class
const Scrapers = require('./Scrapers');

app.use(express.json());
app.use(express.urlencoded({ extended: false }));

app.use(cors())

// api routes
app.get('/',  (req, res) => {
  res.send('welcome!')
})

// web scraper API route
// it accepts just the websiteURL as parameter
app.post('/api/v1/scrape', (req, res) => {
    let productUrl = req.body.url
let scraper = new Scrapers()
scraper.scrapeAmazonStore(productUrl)
.then(data => {
    res.status(200).json({
        status: true,
        message:data
    })
})
.catch(err => {
    res.status(400).json({
        status: false,
        message: err
    })
})
})

// catch 404 and forward to error handler
app.use((req, res, next) => {
  next(res.status(400).json({
    status: false,
    data: 'Bad request'
  }));
});

// error handler
app.use((err, req, res) => {
  // render the error page
  res.status(err.status || 500).json({
    status: false,
    data: 'internal server error'
  });
});

app.listen( process.env.PORT, () =>
console.log(` listening at http://localhost:${process.env.PORT}`)
)

Usage.

For this use-case, this API needs to be very simple and we intend to target one website and scrape specific data.

Amazon store is a great place to start ๐Ÿ˜€ and get the data of a product's price, title and landing-image .

Now let's get what we need

  1. Product url
  2. And the location of the specific information on the website

Implementation.

  • The scrapeAmazonStore method takes the product's url, let's get it

Screenshot_2020-08-16_18-04-52.png

  • To get specific data of the web page, we need to target its HTML, We achieve this by, inspecting the content we need > and copy the xpath of the HTML

Screenshot_2020-08-16_18-05-24.png

Let's write the model ScrapeProduct class:

const puppeteer = require('puppeteer');

class ScrapeProduct{
    async scrapeAmazonStore(url){
        try {
           // we stated ealier that puppeteer library is headless browser, i.e no browser-GUI
           // we start off by launching the browser asychronously
            const browser = await puppeteer.launch({
                headless:true,
                args: [
                  '--no-sandbox'
                ],
              });
            // open a new web page
            const page =  await browser.newPage();
                   // goto the product url that was parsed
                    await page.goto(url);

                    //get product imgUrl
                    // insert the product image xpath
                    // web crawlers understand xpath
            const [el] = await page.$x('//*[@id="landingImage"]');
            const src = await el.getProperty('src');
            const imgUrl = await src.jsonValue();

                    // get product title
                    // insert the product title xpath
            const [el2] = await page.$x('//*[@id="productTitle"]');
            const txt = await el2.getProperty('textContent');
            let title = await txt.jsonValue();



                    // get product price
                   // insert the product price xpath
            const [el3] = await page.$x('//*[@id="priceblock_ourprice"]');
            const txt2 = await el3.getProperty('textContent');
            const price = await txt2.jsonValue();

                 // return an object containing the product's image, title and price
            return{
                imgUrl,
                title,
                price
            }
           // close the headless browser
            browser.close()
        } catch (error) {
            console.log(error)
             return error
        }
    }

}
module.exports = ScrapeProduct

All set and configured , let's test the API ๐Ÿ˜‡:

Screenshot_2020-08-16_18-44-51.png The API successful returns data about the product ๐Ÿ˜Ž ! well this API could be better, in terms of its

  • Response time
  • Robustness to support multiple stores
  • Generic to support all kinds of products etc

Feel free to use the scraperdemo API as a template to build your ideas ๐Ÿ‘ and do drop a star โญ on the scraperdemo project.

Thanks for the audience ๐Ÿค— and connect with me on Github, linkedIn and Twitter.

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