public class MyLink implements RootAction {
    @JavaScriptMethod
    public void setUserId(final String value) {
        userId = value;
}

<st:bind var="instance" value="${it}"/>

instance.setUserId($('#userId')

if(window.jQuery === window.$) { //Is jQuery the active framework?
    $.ajax({
        type: "POST",
        url: url+methodName,
        data: stringify(a),
        contentType: 'application/x-stapler-method-invocation;charset=UTF-8',
        headers: {'Crumb':crumb},
        dataType: "json",
        success: function(data, textStatus, jqXHR) {
            if (callback!=null) {
                var t = {};
                t.responseObject = function() {
                    return data;
                };
                callback(t);
            }
        }
    });
    } else { //Assume prototype should work
    new Ajax.Request(url+methodName, {
        method: 'post',
        requestHeaders: {'Content-type':'application/x-stapler-method-invocation;charset=UTF-8','Crumb':crumb},
        postBody: stringify(a),
        onSuccess: function(t) {
            if (callback!=null) {
                t.responseObject = function() {
                    return eval('('+this.responseText+')');
                };
                callback(t);
            }
        }
    });
}

// KK patch -- handle crumb for POST automatically by adding a header
    if(this.options.method=="post") {
        if(this.options.requestHeaders==undefined)
            this.options.requestHeaders = {};
        crumb.wrap(this.options.requestHeaders);
    }
// KK patch until here