Question

The jsFiddle: http://jsfiddle.net/hbrls/Snn87/12/

I have a verify code field: <input type="text" id="verfy_code" name="verfy_code" class="required" />

and the validation js is:

    $("#aspnetForm").validate({
            rules: {
                verfy_code: {
                    required: function(element) { return check_verfy_code(); }
                }
            },
            messages: {
                verfy_code: { required: "verify code not correct" }
            }
        });
    function check_verfy_code() {
        var flag = false;
        //some ajax to check if verfy_code equalto session["verfy_code"]
        //I've not implemented this, so this function will always return false
        return flag;
    }

The messages never show.

Answer 1

Check the documentation for the required(dependency-callback) option:

The function is executed with the element as it’s only argument: If it
returns true, the element is required.

You are always returning false, therefore the element is never required.

If you return true from your function your dependency callback will work as you expect:

function check_verfy_code() {
    var flag = true;
    //some ajax to check if verfy_code equalto session["verfy_code"]
    //I've not implemented this, so this function will always return false
    return flag;
}

Example: http://jsfiddle.net/jZjFq/