@epegzz/node-scraper

v1.2.0

Published

3 years ago

Scraping websites made easy! A minimalistic yet powerful tool for collecting data from websites.

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epegzz

node scraping scraper

Features

Generator based: It will only scrape as fast as you can consume the results
Powerful HTML parsing: Uses the popular cheerio library under the hood
Easy to test: Uses Axios to make network requests, which can be easily mocked

Installing

using npm

npm install @epegzz/node-scraper --save

using yarn

yarn add @epegzz/node-scraper

Concept

node-scraper is very minimalistic: You provide the URL of the website you want to scrape and a parser function that converts HTML into Javascript objects.

Parser functions are implemented as generators, which means they will yield results instead of returning them. That guarantees that network requests are made only as fast/frequent as we can consume them. Stopping consuming the results will stop further network requests ✨

Example

const scrape = require('@epegzz/node-scraper')

// Start scraping our made-up website `https://car-list.com` and console log the results
//
// This will print:
//   { brand: 'Ford', model: 'Focus', ratings: [{ value: 5, comment: 'Excellent car!'}]}
//   { brand: 'Audi', model: 'A8', ratings: [{ value: 4.5, comment: 'I like it'}, {value: 5, comment: 'Best car I ever owned'}]}
//   ...
;(async function() {
  const scrapeResults = scrape('https://car-list.com', parseCars)
  for await (const carListing of scrapeResults) {
    console.log(JSON.stringify(carListing))
  }
})()

/**
 * https://car-list.com
 *
 * <body>
 *   <ul>
 *     <li class="car">
 *       <span class="brand">Ford</span>
 *       <span class="model">Focus</span>
 *       <a class="ratings" href="/ratings/ford-focus">show ratings</a>
 *     </li>
 *     ...
 *   </ul>
 * </body>
 */
async function* parseCars({ find, follow, capture }) {
  const cars = find('.car')
  for (const car of cars) {
    yield {
      brand: car.find('.brand').text(),
      model: car.find('.model').text(),
      ratings: await capture(car.find('a.ratings').attr('href'), parseCarRatings)
    }
  }
  follow(find('.next-page'))
}

/**
 * https://car-list.com/ratings/ford-focus
 *
 * <body>
 *   <ul>
 *     <li class="rating">
 *       <span class="value">5</span>
 *       <span class="comment">Excellent car!</span>
 *     </li>
 *     ...
 *   </ul>
 * </body>
 */
function* parseCarRatings({ find }) {
  const ratings = find('.rating')
  for (const rating of ratings) {
    yield {
      value: rating.find('.value').text(),
      comment: rating.find('.comment').text(),
    }
  }
}

API

Usage

Here's the basic usage:

  // import scraper
  const scrape = require('@epegzz/node-scraper')

  // define a parser function
  function* parser() {
    // ...
  }

  // call scraper with URL and parser
  const scrapeResults = scrape('https://some-website.com', parser)

  // consume scrape results
  for await (const scrapedItem of scrapeResults) {
    console.log(JSON.stringify(scrapedItem))
  }

Instead of calling the scraper with a URL, you can also call it with an Axios request config object to gain more control over the requests:

const scrapeResults = scrape({
  url: 'https://some-website.com',
  timeout: 5000,
}, parser)

Creating a parser function

A parser function is a synchronous or asynchronous generator function which receives three utility functions as argument: find, follow and capture.

A fourth parser function argument is the context variable, which can be passed using the scrape, follow or capture function.

Whatever is yielded by the generator function, can be consumed as scrape result.

async function* parseCars({ find, follow, capture }) {
  const cars = find('.car')
  for (const car of cars) {
    yield {
      brand: car.find('.brand').text(),
      model: car.find('.model').text(),
      ratings: await capture(car.find('a.ratings').attr('href'), parseCarRatings)
    }
  }
  follow(find('a.next-page').href)
}

;(async function() {
  const scrapeResults = scrape('https://car-list.com', parseCars)
  for await (const car of scrapeResults) {
    // whatever is yielded by the parser, ends up here
    console.log(JSON.stringify(car))
  }
})()

`find(selector, [node])` Parse the DOM of the website

The find function allows you to extract data from the website. It's basically just performing a Cheerio query, so check out their documentation for details on how to use it.

Think of find as the $ in their documentation, loaded with the HTML contents of the scraped website.

Example:

  // yields the href and text of all links from the webpage
  for (const link of find('a')) {
    yield {
        linkHref: link.attr('href'),
        linkText: link.text(),
    };
  }

The major difference between cheerio's $ and node-scraper's find is, that the results of find are iterable. So you can do for (element of find(selector)) { … } instead of having to use a .each callback, which is important if we want to yield results.

The other difference is, that you can pass an optional node argument to find. This will not search the whole document, but instead limits the search to that particular node's inner HTML.

`follow(url, [parser], [context])` Add another URL to parse

The main use-case for the follow function scraping paginated websites. In that case you would use the href of the "next" button to let the scraper follow to the next page:

async function* parser({ find, follow }) {
  ...
  follow(find('a.next-page').attr('href'))
}

The follow function will by default use the current parser to parse the results of the new URL. You can, however, provide a different parser if you like.

`capture(url, parser, [context])` Parse URLs without yielding the results

The capture function is somewhat similar to the follow function: It takes a new URL and a parser function as argument to scrape data. But instead of yielding the data as scrape results it instead returns them as an array.

This is useful if you want add more details to a scraped object, where getting those details requires an additional network request:

async function* parseCars({ find, follow, capture }) {
  const cars = find('.car')
  for (const car of cars) {
    yield {
      brand: car.find('.brand').text(),
      model: car.find('.model').text(),
      ratings: await capture(car.find('a.ratings').attr('href'), parseCarRatings)
    }
  }
}

In the example above the comments for each car are located on a nested car details page. We are therefore making a capture call. All yields from the parseCarRatings parser will be added to the resulting array that we're assigning to the ratings property.

Note that we have to use await, because network requests are always asynchronous.

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