How to 

There's no need to parse the URL as a string. You can let the browser do it for you (and even modify the parameters this way):

const params = new URL(document.URL).searchParams;
// checking for params
params.has("u") 
// getting a param
params.get("username")

Fabian Iwand

And the best thing: you can convert the URL object back to a URL string, which is great if you need to safely construct and sanitize a URL.

Thank you very much for your feedback. I'll test it.

By the way, I think you may want to use document.baseURI instead of document.URL (the latter is the sandboxed iframe's URL).

Thanks I've got a new function get_parameter()