How do I create a site that will auto click a button on another site till on another page loads in then I auto refill the open page

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Javascript

I have tried using Xmlhttprequest but nothing is working.
I tried getting the Dom object load so dat I can click on it . don't even know if am on the right path

What I have tried:

Xhr=new Xmlhttprequest ();
Xhr.onreadystatechange=function (){ if (Xhr.readystate==4){
if (Xhr.status==200){
Let parser=new Domparser();
Let va=parser.parserFromString(Xhr.response, console.log(va);
}
else if (Xhr.status==404){
Console.log('file not found);
}}}
Xhr.open('get',url of the site,false);
Xhr.send();