detecting a redirect with javascript - how?
Yes, you can do this quite easily in Javascript. It'd look something like:
var xhr = new XMLHttpRequest();xhr.onload = function() { if (this.status < 400 && this.status >= 300) { alert('this redirects to ' + this.getResponseHeader("Location")); } else { alert('doesn\'t redirect '); }}xhr.open('HEAD', '/my/location', true);xhr.send();Unfortunately, this only works on your own server, unless you hit a server with CORS set up. If you wanted to work uniformly across any domain, you're going to have to do it server-side.
Here is simple solution for your question.
x.addEventListener('readystatechange',function(){ const url = 'https://your/request/url'; if(this.responseURL != url){ alert('redirected'); }});