jQuery plugin to equalize form element widths

jquery.fapi_widths.js

/**
 * Form Element Width Equalizer Plugin (Optimized for Drupal FAPI)
 *
 * Adjusts the widths of child elements to a set pixel dimension.
 *
 * Makes all text fields and text areas (or other as specified in
 * options.elements) equal widths by subracting the css properties of: margin,
 * border and padding from each element.
 *
 * If width is omitted then all elements will have their width matched to $(this)
 *
 * @param options
 * - width: string or int
 *   Optional.  Defaults to the outer
 * - width: either a jQuery selector or an width (N or Npx), which is the
   desired outerWidth of all elements, if omitted the width of the $(this) will
   be used.
 * - elements: the children of $(this); is passed to $(this).find(); defaults to
 *   .form-text, .form-textarea-wrapper
 * - reset: ignores width and returns all elements to their original widths
 *
 * @return $(this)
 *
 * @code
 *  $('#screening-node-form').fapiWidths({width: 470});
 * @endcode
 *
 * @author Aaron Klump, In the Loft Studios, LLC
 * @see http://www.intheloftstudios.com
 * @see http://gist.github.com/3276507
 * @see http://blog.jquery.com/2012/08/16/jquery-1-8-box-sizing-width-csswidth-and-outerwidth/
 */
(function( $ ) {
  $.fn.fapiWidths = function(options) {

    var $parent = $(this);

    // Handle if options.width has been passed
    if (options && options.hasOwnProperty('width')) {
      if (options.width.width) {
        // If we passed an object with method .width() then parse it.
        options.width = options.width.width();
      }
      options.width = parseInt(options.width, 10);
    }

    // Create some defaults, extending them with any options that were provided
    var settings = $.extend( {
      'elements'         : '.form-text, .form-textarea-wrapper',
      'width'            : 'auto',
      'reset'            : false,
      'max'              : 0
    }, options);

    var $formElements = $parent.find(settings.elements);
    if (!$formElements.length) {
      return $(this);
    }

    // Delay this to avoid a performance hit if not necessary
    if (settings.width === 'auto') {
      settings.width = parseInt($parent.width(), 10);
    }

    $formElements.filter(':visible').each(function() {
      var $element     = $(this);

      // First time register the original width
      if (!$element.data('fapi-reset')) {
        $element.data('fapi-reset', $element.outerWidth(true));
      }
      var newWidth;
      if (settings.reset) {
        if ($element.data('fapi-reset')) {
          newWidth = $element.data('fapi-reset');
        }
      }
      else {
        var box = {};
        box.lm      = parseInt($element.css('marginLeft'));
        box.rm      = parseInt($element.css('marginRight'));
        var boxSizing = $element.css('box-sizing');
        if (boxSizing !== 'border-box') {
          box.lb      = parseInt($element.css('borderLeftWidth'));
          box.lp      = parseInt($element.css('paddingLeft'));
          box.rp      = parseInt($element.css('paddingRight'));
          box.rb      = parseInt($element.css('borderRightWidth'));
          newWidth    = settings.width - (box.lm + box.lb + box.lp + box.rp + box.rb + box.rm);
        }
        else {
          newWidth    = settings.width - (box.lm + box.rm);
        }
        newWidth   += 'px';
      }
      if (settings.max && parseInt(newWidth, 10) > settings.max) {
        newWidth = settings.max + 'px';
      }
      if (newWidth) {
        $element.css('width', newWidth);
      }
    });
    return $(this);
  };
})(jQuery);