Temporary fix for Issue : Trigger function on Page's requestfinished event #93

Created by: sebastienfi

Quick PR to expose Page's requestfinished event.

Temporary fix for https://github.com/yujiosaka/headless-chrome-crawler/issues/93 @yujiosaka your solution expose the whole page is way better.

This scenario allow to intercept the request and do something with the response without having to download the ressource a second time, which is, the official way of doing this.

const HCCrawler = require('headless-chrome-crawler')
var fs = require('fs')

HCCrawler.launch({ 
  // Function to be evaluated in browsers
  evaluatePage: (() => ({
    title: $('title').text()
  })),
  // Function to be called with evaluated results from browsers
  onSuccess: (result => {
    console.log(result)
  }),  
})
  .then(crawler => {

    crawler.on('pagerequestfinished', async request => {
        const url = request.url()
        // Matches images.
        const match = /.*\.(jpg|png|gif)$/.exec(url)
        if (match && match.length === 2) {
          const split = url.split('/')
          const filename = split[split.length - 1]
          const response = request.response()
          const buffer = await response.buffer()
          fs.writeFileSync(`./tmp/${filename}`, buffer, 'base64')
        }
    })

    crawler.queue({
      maxDepth: 1,
      skipDuplicates: true,
      url: `http://www.example.com`
    })

    crawler.onIdle() // Resolved when no queue is left
      .then(() => crawler.close()) // Close the crawler
  })