scp.js

// Thanks, http://stackoverflow.com/a/487049
function addSearchParam(key, value) {
    key = encodeURI(key); value = encodeURI(value);

    var kvp = document.location.search.substr(1).split('&');
    var i=kvp.length; var x;
    while (i--) {
        x = kvp[i].split('=');
        if (x[0]==key) {
            x[1] = value;
            kvp[i] = x.join('=');
            break;
        }
    }
    if(i<0) {kvp[kvp.length] = [key,value].join('=');}

    //this will reload the page, it's likely better to store this until finished
    return kvp.join('&');
}