so I have a question, which maybe it's a little ez, but... I don't know hehe, so, how do you get a value that's in the domain? like:
https://example.com?test=helloworld
how do I get the value of the "test" variable that is there?
You probably mean https://example.com?test=helloworld including a ?.
Reading Value from URL
const url = new URL('https://example.com?test=helloworld');
console.log(url.searchParams.get("test")); // prints: helloworld
And to get the current URL you can use window.location.href.
Add Value to URL
const url = new URL('https://example.com');
url.searchParams.append('test', 'helloworld');
console.log(url.href); // prints: https://example.com?test=helloworld
Have a look at the URL API on the MDN documentation.