how to replace part of the URL with JavaScript?
The only way to update the displayed URL without reloading the page is history.pushState
window.history.pushState('', '', '/your-new-url');
My version. Works fine for me.
let url = window.location.toString();
window.history.pushState('', '', url.replace(searching_string, new_string));
location.href = location.href.replace(
'function=search&', 'function=loginsearch&user=admin&password=admin&')
var url = window.location.toString();
window.location = url.replace(/function=search/, 'function=loginsearch&user=admin&password=admin');