Validate WordPress default comment form using jQuery Validation Plugin

jquery-wp-comment-validation.js

// Step 1 enqueue jQuery Validation Plugin (http://cdn.jsdelivr.net/jquery.validation/1.15.0/jquery.validate.js) on function.php
// Step 2 enqueue jQuery this js file
// enjoy 
jQuery(function($) {
  $('#commentform').validate({

    rules: {
      author: {
        required: true,
        minlength: 2
      },

      email: {
        required: true,
        email: true
      },

      comment: {
        required: true,
        minlength: 20
      }
    },

    messages: {
      author: "Please fill the required field",
      email: "Please enter a valid email address.",
      comment: "Please fill the required field"
    },

    errorElement: "div",
    errorPlacement: function(error, element) {
      element.after(error);
    }

  });
});