Minimum Amount Validator for 2Dialog Forms

MinimumAmountValidator.js

var MinimumAmountValidator = Class.create({

    settings: {
      "minimum_amount": 1,
      "checkbox_id"   : null,
      "input_id"      : null,
      "only_integer"  : false
    },

    initialize: function( settings ){
      Object.extend(this.settings, settings);
      this.$free_donation_checkbox   = $(this.settings.checkbox_id);
      this.$free_donation_text_input = $(this.settings.input_id);
      this.$free_donation_label      = this.$free_donation_text_input.next();
      this.listenEvents();
    },

    listenEvents: function(){
      var self = this;
      $$('input[type="radio"]').each(function(radio){
        radio.observe('click', self.validateIfChecked.bind(self));
      });
      this.$free_donation_text_input.observe('focus', self.validateIfChecked.bind(self));
      this.$free_donation_text_input.observe('change', self.validateAmount.bind(self));
    },

    validateIfChecked: function(){
      if( this.$free_donation_checkbox.checked ){
        $$('input[id*=submitButton_]')[0].hide();
        this.validateAmount();
      } else {
        this.removeErrorMessage();
        $$('input[id*=submitButton_]')[0].show();
      }
    },

    validateAmount: function(){

      var value          = this.$free_donation_text_input.getValue();
      var minimum_amount = this.settings.minimum_amount;

      if( this.settings.only_integer ){
        value = this.integerize( value );
        // update the input value, but don't fire the change event...
        this.$free_donation_text_input.value = value;
      }

      this.removeErrorMessage();
      this.$free_donation_text_input.removeClassName('form-error');

      if( value < minimum_amount ){
        this.insertErrorMessages();
        this.$free_donation_text_input.addClassName('form-error');
        $$('input[id*=submitButton_]')[0].hide();
      } else {
        $$('input[id*=submitButton_]')[0].show();
      }
    },

    integerize: function( amount ){
      amount = amount.replace(',', '.') * 1;
      amount = Math.round(amount);
      return amount;
    },

    insertErrorMessages: function(){
      var message = '<span id="minimum_amount_error" style="color:red; margin-left: 10px; display: block;">The minimum amount is $'+this.settings.minimum_amount+'</span>';
      this.$free_donation_checkbox.ancestors()[0].insert(message);
      var submit_button_error_message = '<span id="minimum_amount_submit_button_error" style="color:red; margin-left: 10px">We\'re sorry. The minimum online donation amount is $'+this.settings.minimum_amount+'. Thank you.</span>';
      $$('input[id*=submitButton_]')[0].ancestors()[0].insert(submit_button_error_message);
    },

    removeErrorMessage: function(){
      if( $('minimum_amount_error') ){
        $('minimum_amount_error').remove();
      }
      if( $('minimum_amount_submit_button_error') ){
        $('minimum_amount_submit_button_error').remove();
      }
    }

  });

/* Update the following settings with the correct values */
new MinimumAmountValidator({
	minimum_amount: 12, // update this
	checkbox_id   : "frmItem_158_963", // update this
	input_id      : "donation_value_198_963", // update this
	only_integer  : true // update here, if not, default is false
});