Adding a rule for jQuery validation plugin

I'm using following rules to validate the username using jQuery validation method. I want to add another rule that username should contain only alphanumeric and underscore character. How can i add add开发者_如何学JAVAitional method for that rule. Is it possible that if user gives less than 4 characters, then I print the minimum length error message, and if the user gives invalid characters, then I give the invalid character error message? Thanks.

$(document).ready(function() {
$("#sform").validate({
            rules: {
                username: {
                    required: true,
                    minlength: 4
                }
            },

            messages: {
                username: "Minimum length 4.",              
            }
        });
    });

---

add like below

jQuery.validator.addMethod("alphanumeric", function(value, element) {
    return !jQuery.validator.methods.required(value, element) || /^[a-zA-Z0-9_]+$/i.test(value);
}
, "Letters, numbers or underscores only please"); 

and apply below

$('validatorElement').validate({
    rules : {
        username : { alphanumeric : true }
    }
});

---

Using remote ajax validation do this

$("#sform").validate({
    rules: {
    username: {
        required: true,
        minlength: 4,
        remote: 'alphanumertic.php'
        //check on server
    }
    },
    messages: {
    username: "Minimum length 4.",              
    }
});

Probably the best way is to validate using regular expression which can be found on

jQuery validate: How to add a rule for regular expression validation?

Regular Expression for alphanumeric and underscores

---

The validation plugin comes with additional-methods.js, which includes an alphanumeric plus underscore validation:

http://ajax.aspnetcdn.com/ajax/jquery.validate/1.10.0/additional-methods.js

Same rules as above:

$('validatorElement').validate({
    rules: {
        username: { alphanumeric : true }
    }
});

---

_{Old question but I am adding my answer so that one can get help}
One can use following:

• create a function that will encapsulate our validation test, with the following signatures: function mytest(value, element, params){...}

• After we have the function established, we can then attach it to the jQuery Validation plug-in. To do this, we call the validator object's addMethod() function.

My Code:

$(document).ready(function() { 
  // other code
  // :  
  // :  
  $.validator.addMethod(
    "passwd",
     function(value, element, regexp) {
        var re = new RegExp(regexp);
           return this.optional(element) || re.test(value);
     },
    "Invalid input"
   );

  $("#add_user_form").validate({
      rules:{
        user_name: {
           required: true,
           minlength: 5,
           maxlength: 15,
           noSpace: true
        },
        password: {
          required: true,
          minlength: 8,
          passwd: "((?=(.*\\d.*){2,})(?=(.*[a-zA-Z].*){2,})(?=(.*[@#$(){}!~,.!^?/|+=-_%].*){2,}).{8,20})"
      }
    },

    messages:{
       user_name: {
         required: "*",
         minlength: " at least 5 characters",
         maxlenght: " only 15 characters",
         noSpace: " No space Please"
       },
       password: {
         required: "*",
         minlength: " Your password must be at least 8 characters long",
         passwd: " Invalid Password choice"
       }
 }); 
 //
 // more code in document.ready 

good links:
Starting With jQuery - How to Write Custom Validation Rules
How to add a rule for regular expression validation?