如何自动检查网站上某个元素的实例并返回一个数值

Question

I need some kind of software that allows me to script an automated process that opens a specific website, checks how many instances of a certain element (say, an H1 element, or a button) there are and return a number. So that it can then see if there's one more or less than the last time it checked and give out an alert that something has changed.

And I need to do this from the client's side, on his/her computer, and not the server, so it can't be coded into the website.*

Somebody recommended I try WinTask and I've been playing with it for a couple of weeks and gotten interesting results but, apparently, there's no way I can get it to "read" certain elements on a website and "count" them... All I could get it to do, for instance, is to click on all links or buttons on a website... which could work for what I need, if only it was able to count how many of these elements there are and return a number value; but it seems it can't.

I was also recommended Selenium... But on that one I haven't even been able to set it up correctly and run a simple script!

I'm open to all ideas! Thanks!

*EDIT: To be clearer about this point: I literally can't add any code to the websites in question, or edit them in any way, as they're thrid-party websites to which I have no access. You see, the idea is that there are certain job postings that appear on these websites and one has to check the websites every so often in order to see what's available. The idea of this automated script would be to refresh the website every 30 mins or so, read how many posted items there are and, knowing how many there were last time it checked, give out an alert when the difference is +1 or more items.

Answer 1

You can use jquery or javascript to get the results.

This is without using the GET method for the sake of showing you results. Then use maybe a cookie to store the value of the page and results and compare the numbers by retrieving the cookies values.

 console.log($('h1').length); console.log($('span').length); console.log($('.anotherclass').length);

 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <h1>Here are some examples</h1> <span class="someclass">First Test</span> <span class="anotherclass">Second Test</span> <span class="anotherclass">Third Test</span>

Update:

It is limited since cookies are involved and that is a security issue embedding codes.

But say you get the contents and save a cookie of old posts and compare that to the amount of current posts... we can then write a code something like so.

 var newjobs = document.getElementById('newjobs'); oldposts = 50; currentposts = 73; newposts = (currentposts - oldposts); if ( newposts > 0){ newjobs.innerHTML = 'There are ' + newposts + ' new job listings'; } else { newjobs.innerHTML = 'There are no new job listings'; }

 <p id="newjobs"> </p>