how to append query string to url javascript code example

Example: js add query param

function setParam(uri, key, val) {
    return uri
        .replace(RegExp("([?&]"+key+"(?=[=&#]|$)[^#&]*|(?=#|$))"), "&"+key+"="+encodeURIComponent(val))
        .replace(/^([^?&]+)&/, "$1?");
}