form-validator.js

FormValidator = function(form){
  this.forms = form || $("form[data-validate=true]");
  this.setDefaults = function(){
    $.validator.setDefaults({
      errorElement: "span"
    })
    $.extend(jQuery.validator.messages, {
      required: "Mandatory Field"
    })
  }

  this.validateForms = function(f){
    f.validate();
  }

  // "data-rules"=>{messages: {required: 'Required input'}}.to_json
  this.setRules = function(newRules){
    $("input", this.forms).each(function(i,v){
      ele = $(v);
      rules = newRules || ele.data("rules")
      if(rules){
        ele.rules("add", rules)
      }
    })
  }
  this.setAll = function(){
    this.setDefaults()
    this.validateForms(this.forms)
    this.setRules()
  }
  this.setAll()
}
$(function(){
  var validator = new FormValidator();
})

<%= form_for @object ,data: {validate: true} do |f| %>
<%= f.text_field :email, class: "required", data:{rules: {messages: {required: "Please enter email"}}.to_json} %>
<% end %>