store utm_source parameter to localStorage

<script type="text/javascript">
//Function to save value of url parameter
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, " "));
}
// Code for localStorage/sessionStorage.
if(typeof(Storage) !== "undefined") {
    // check if localStorage source item is null
    if (localStorage.getItem('source') === null) {
         var source =  getParameterByName("utm_source");

        // store value for later use
        localStorage.setItem("source", source);
    }

    var field = document.querySelector('input#hiddensource');
    if (field)
        field.value = localStorage.getItem("source");
        //clear value after it was injected (optional)
        //localStorage.removeItem("source");
}
else {
// Sorry! No Web Storage support..
}
</script>