javascript獲取querystring

function QueryString(fieldName) {
    var urlString = document.location.search;
    while (urlString.indexOf("& ") >= 0) {
        urlString = urlString.replace("& ", "&");
    }
    while (urlString.indexOf("? ") >= 0) {
        urlString = urlString.replace("? ", "?");
    }
    if (urlString != null) {
        var typeQu = "?" + fieldName + "=";
        var urlEnd = urlString.toUpperCase().indexOf(typeQu.toUpperCase());
        if (urlEnd == -1) {
            typeQu = "&" + fieldName + "=";
            urlEnd = urlString.toUpperCase().indexOf(typeQu.toUpperCase());
        }
        if (urlEnd != -1) {
            var paramsUrl = urlString.substring(urlEnd + typeQu.length);
            var isEnd = paramsUrl.indexOf('&');
            if (isEnd != -1) {
                return paramsUrl.substring(0, isEnd);
            }
            else {
                return paramsUrl;
            }
        }
        else
            return "";
    }
    else
        return "";
}