svgclass.js

(function($){

  /* addClass shim
   ****************************************************/
  var addClass = $.fn.addClass;
  $.fn.addClass = function(value) {
    var orig = addClass.apply(this, arguments);
 
    var elem,
      i = 0,
      len = this.length;

    for (; i < len; i++ ) {
      elem = this[ i ];
      if ( elem instanceof SVGElement ) {
        var classes = $(elem).attr('class');
        if ( classes ) {
            var index = classes.indexOf(value);
            if (index === -1) {
              classes = classes + " " + value;
              $(elem).attr('class', classes);
            }
        } else {
          $(elem).attr('class', value);
        }
      }
    }
    return orig;
  };

  /* removeClass shim
   ****************************************************/
  var removeClass = $.fn.removeClass;
  $.fn.removeClass = function(value) {
    var orig = removeClass.apply(this, arguments);

    var elem,
      i = 0,
      len = this.length;

    for (; i < len; i++ ) {
      elem = this[ i ];
      if ( elem instanceof SVGElement ) {
        var classes = $(elem).attr('class');
        if ( classes ) {
          var index = classes.indexOf(value);
          if (index !== -1) {
            classes = classes.substring(0, index) + classes.substring((index + value.length), classes.length);
            $(elem).attr('class', classes);
          }
        }
      }
    }
    return orig;
  };

  /* hasClass shim
   ****************************************************/
  var hasClass = $.fn.hasClass;
  $.fn.hasClass = function(value) {
    var orig = hasClass.apply(this, arguments);

    var elem,
      i = 0,
      len = this.length;
        
    for (; i < len; i++ ) {
      elem = this[ i ];
      if ( elem instanceof SVGElement ) {
        var classes = $(elem).attr('class');

        if ( classes ) {
          if ( classes.indexOf(value) === -1 ) {
            return false;
          } else {
            return true;
          }
        } else {
            return false;
        }
      }
    }
    return orig;
  };
})(jQuery);

I added a couple trim() functions to the returns. In a circumstance where I was triggering the add/removeClass function within an interval loop, a single white space would occur each time. Trim resolved this. See my fork here