Simple Scraper

scraper.js

'use strict';

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

/**
 * The default constructor
 */
function Scraper() {

}

/**
 * Returns a http get request promise
 * 
 * @param  {Object}  req     The request definition
 * @return {Promise} promise The get request promise
 */
Scraper.prototype.get = function(req) {
  return request(req);
}

/**
 * Returns a cheerio instance loaded with the given html body
 * 
 * @param  {String}   body The html body
 * @return {Function} $    The cheerio instance
 */
Scraper.prototype.load = function(body) {
  return cheerio.load(body);
}

/**
 * Returns a promise of a request call
 * 
 * @param  {String}  uri The request uri
 * @param  {Object}  qs  The request query string 
 * @return {Promise} promise The request promise
 */
Scraper.prototype.prepare = function(uri, qs) {
  var req = {
    uri:             uri,
    qs:              qs,
    simple:          false,
    transform:       this.load,
    followRedirects: false
  };

  return this.get(req).then(this.scrape);
}

/**
 * Executes the scrape chain: 
 * request -> cheerio load -> scrape -> transform
 * 
 * @param  {Array}   promises The promises array
 * @return {Promise} promise  The execution result
 */
Scraper.prototype.execute = function(promises) {
  var self = this;
  return Promise.all(promises).then(function(result) {
    return self.transform(result);
  });
}

/**
 * The scrape method.
 * This is the abstract method that should be implemented by all the scrapers.
 * It performs a html body scrape.
 * 
 * @param  {Function} $ The cheerio instance
 * @return {Array}    result The scrape result
 */
Scraper.prototype.scrape = function($) {
  throw new TypeError('scrape() method must be implemented');
}

/**
 * The transform method.
 * This is the abstract method that should be implemented by all the scrapers.
 * It transform the scrape result in a array of objects.
 * 
 * @param  {Array} result The scrape result
 * @return {Array} normalized An array of normalized data
 */
Scraper.prototype.transform = function(result) {
  throw new TypeError('transform() method must be implemented');
}

module.exports = Scraper;