You would have to use this with a cronjob or something of the sort

scrapehn.js

var casper = require('casper').create({viewportSize: {width: 960, height: 600}});
var fs = require('fs');

casper.start('https://news.ycombinator.com/', function() {
    var now = this.fetchText('#hnmain');
    var old = fs.read('old.txt');
    if (old !== now) {
        casper.open('http://text-compare.com/', {
            method: 'post',
            data:   {'text1': old, 'text2':  now}
        }).then(function () {
            casper.captureSelector('diff' + Date.now() + '.png', '#top');
            // Code to notify you here, e.g. IFTTT API, mail, etc
        });
        fs.write('old.txt', now, 'w');
    }
}).run();