Javascript：将第二个下拉选项附加到URL

Hi I have two dropdowns in my webpage. How do I append the second dropdown selection to the URL without using.

window.location.href +="&selected2="+value2;

please tell me what change I must to the the function setsecondparam where value1 is the selection from the first dropdown.

function seturl(sel){        
var value = sel.options[sel.selectedIndex].value;
window.location.href = "website.php?selected1="+value;
}

function setsecondparam(sel,value1) 
{
 var value2 = sel.options[sel.selectedIndex].value;

 window.location.href ="website.php?selected1="+value1+"&selected2="+value2;
}

Thanks in advance

It's better to use one function. I wrote it more or less in ES5, you can change it to ES6 if you use babel.

function insertParams (key, value) {
    let search = window.location.search;
    let regex = new RegExp(key+"=[^\&]*");

    search = search.replace(regex, key + '=' + value);
​
    if (!regex.test(search)) {
        search += (search.length > 0 ? '&' : '?') + key + '=' + value;
    }
​
    document.location.search = search;
}