ES6 javascript to download certificates from proprofs.com via webscraping. Supply a base integer to the start() method (typically a certificate you know of), and it will either increment the value and download or decrement, which you can change in the _modifyId() function. It limits to 100 and then quits downloading, this can be altered.

download-certs-proprofs.js

const request = require('request');
const cheerio = require('cheerio');
const http = require('https');
const fs = require('fs');


class CertificateDownloader {

    constructor() {
        this.limit = 100;
        this.downloadCount = 0;
        this.skippedImageCount = 0;
        this.imageExtension = '.jpg';
        this.currentId = -1;
        this.rootUrl = 'https://www.proprofs.com/';
    }

    _modifyId() {
        this.currentId--;
    }

    _doesFileExist() {
        return fs.existsSync(`${this.currentId}${this.imageExtension}`);
    }

    _skipDownload() {
        console.log(`${this.currentId}${this.imageExtension} already exists, skipping...`);
        this._modifyId();
        this.skippedImageCount++;
        this.start(this.currentId);
    }

    start(idToStartWith) {
        let self = this;
        if (typeof idToStartWith !== 'number') throw new Error('idToStartWith is required, and to be a number');


        self.currentId = idToStartWith;

        if (this._doesFileExist())
            return this._skipDownload();

        if (this.downloadCount >= this.limit)
            return console.log('Limit met, quitting.');

        console.log(`Getting html for ${this.currentId}, download count ${this.downloadCount}, limit: ${this.limit}, skipped images: ${this.skippedImageCount}...`);
        request(`${this.rootUrl}/quiz-school/usercertificate.php?id=${this.currentId}`, (err, response, body) => {

            if (response.statusCode === 404 || response.statusCode === 500) {
                console.log(`Got a status code of: ${response.statusCode}. Trying next...`);
                self._modifyId();
                return self.start(self.currentId);
            }

            const $ = cheerio.load(body);
            let img = $('body').find('img#certImage');
            let src = `${this.rootUrl}${img[0].attribs.src}`;


            console.log('Getting image...');
            let file = fs.createWriteStream(`${this.currentId}${this.imageExtension}`);

            http.get(src, function(response) {
                response.pipe(file);
                console.log('Done!');
                self._modifyId();
                self.downloadCount++;
                self.start(self.currentId);
            });
        });
    }
}

let downloader = new CertificateDownloader();
downloader.start(152895196);