Backbone: Live Form Validation

gistfile1.js

_.extend(Backbone.View.prototype, {
  checkInput: function (e, target, submitBtn) {
    var _this = this;
    var error = 0;
    submitBtn = submitBtn || '.submit';
    $('span.error').remove();
    $('.error').removeClass('error');
    _.each(this.fields, function (field, i, list) {
      var $el = $(field.$el);
      field.default = field.default || '';
      var curval;
      switch (field.type) {
      case 'checkbox':
        curval = ($el[0].checked) ? 1 : '';
        break;
      case 'text-container':
        curval = $el.text();
        break;
      case 'attribute':
        curval = $el.attr(field.attr);
        break;
      case 'text':
      case 'textarea':
      case 'html':
      case 'radio':
      case 'number':
      case 'password':
      default:
        curval = $el.val();
        break;
      }
      var pass = true;
      // mirrors are text elements that mirror the content of this field
      if (field.mirrors) {
        _.each(field.mirrors, function (mirror, i) {
          $('#' + mirror).text(curval);
        });
      }
      // computes is a callback to be executed with the current value
      if (field.computes) {
        this[field.computes](curval);
      }
      // requires further values - must be an array
      if (field.requires && curval !== undefined && curval !== field.default) {
        _.each(field.requires, function (field) {
          _this.fields[field].required = true;
        });
      } else if (field.requires) {
        _.each(field.requires, function (field) {
          _this.fields[field].required = false;
        });
      }
      // specifically required to be checked online for validity
      if (field['check-online']) {
        var checkpass = function (val) {
          pass = val;
        };
        field.pass(curval, checkpass);
      } else {
        // console.log('value to check: ' + curval);
        pass = field.pass(curval);
      }
      //console.log('checking field ' + field.label + ', required: ' + field.required + ' which returns ' + pass);
      if (field.required && !pass) {
        error++;
        var target_id = (e) ? $(e.target).attr('id') : target.attr('id');
        if (target_id && target_id === $el.attr('id')) {
          if (field.suppress_errors) {
            $el.addClass('error');
          } else {
            $el.after('<span class="error">' + (field.error || field.label + ' is required') + '</span>');
          }
        }
      } else if (!pass && curval !== '') {
        error++;
        if (e && $(e.target).attr('id') === $el.attr('id')) {
          $el.addClass('error').after('<span class="error">' + (field.error || field.label + ' is required') + '</span>');
        }
      } else {
        $el.removeClass('error');
      }
    }, this);
    if (error === 0) {
      $('span.error').remove();
      $(submitBtn).attr('disabled', false);
    } else {
      $(submitBtn).attr('disabled', 'disabled');
    }
  }
});