query_string.js

function getParameterByName(name) {
    name = name.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");
    var regex = new RegExp("[\\?&]" + name + "=([^&#]*)"),
        results = regex.exec(location.search);
    return results == null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "));
}

// assuming a url along the lines of:
// http://www.example.com/index.html?action=win
var action = getParameterByName("action");

if(action && action == "win") {
  // You've won!
}