jQuery Validate Plugin - How to create a simple custom rule?

You can create a simple rule by doing something like this:

jQuery.validator.addMethod("greaterThanZero", function(value, element) {
    return this.optional(element) || (parseFloat(value) > 0);
}, "* Amount must be greater than zero");

And then applying this like so:

$('validatorElement').validate({
    rules : {
        amount : { greaterThanZero : true }
    }
});

Just change the contents of the 'addMethod' to validate your checkboxes.

$(document).ready(function(){
    var response;
    $.validator.addMethod(
        "uniqueUserName", 
        function(value, element) {
            $.ajax({
                type: "POST",
                url: "http://"+location.host+"/checkUser.php",
                data: "checkUsername="+value,
                dataType:"html",
                success: function(msg)
                {
                    //If username exists, set response to true
                    response = ( msg == 'true' ) ? true : false;
                }
             });
            return response;
        },
        "Username is Already Taken"
    );

    $("#regFormPart1").validate({
        username: {
            required: true,
            minlength: 8,
            uniqueUserName: true
        },
        messages: {
            username: {
                required: "Username is required",
                minlength: "Username must be at least 8 characters",
                uniqueUserName: "This Username is taken already"
            }
        }
    });
});

Thanks, it worked!

Here's the final code:

$.validator.addMethod("greaterThanZero", function(value, element) {
    var the_list_array = $("#some_form .super_item:checked");
    return the_list_array.length > 0;
}, "* Please check at least one check box");

Step 1 Included the cdn like

     <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>

     <script src="http://ajax.aspnetcdn.com/ajax/jquery.validate/1.11.1/jquery.validate.min.js"></script>

Step 2 Code Like

  $(document).ready(function(){
        $("#submit").click(function () {
              $('#myform').validate({ // initialize the plugin
                rules: {
                    id: {
                        required: true,
                        email: true
                    },
                    password: {
                        required: true,
                        minlength: 1
                    }
                },
                messages: {
                    id: {
                        required: "Enter Email Id"

                    },
                    password: {
                        required: "Enter Email Password"

                    }
                },
                submitHandler: function (form) { // for demo
                    alert('valid form submitted'); // for demo
                    return false; // for demo
                }
            });
       }):
  });