fabric.js/src/util/lang_class.js

(function() {

  var slice = Array.prototype.slice, emptyFunction = function() { },

      IS_DONTENUM_BUGGY = (function() {
        for (var p in { toString: 1 }) {
          if (p === 'toString') {
            return false;
          }
        }
        return true;
      })(),

      /** @ignore */
      addMethods = function(klass, source, parent) {
        for (var property in source) {

          if (property in klass.prototype &&
              typeof klass.prototype[property] === 'function' &&
              (source[property] + '').indexOf('callSuper') > -1) {

            klass.prototype[property] = (function(property) {
              return function() {

                var superclass = this.constructor.superclass;
                this.constructor.superclass = parent;
                var returnValue = source[property].apply(this, arguments);
                this.constructor.superclass = superclass;

                if (property !== 'initialize') {
                  return returnValue;
                }
              };
            })(property);
          }
          else {
            klass.prototype[property] = source[property];
          }

          if (IS_DONTENUM_BUGGY) {
            if (source.toString !== Object.prototype.toString) {
              klass.prototype.toString = source.toString;
            }
            if (source.valueOf !== Object.prototype.valueOf) {
              klass.prototype.valueOf = source.valueOf;
            }
          }
        }
      };

  function Subclass() { }

  function callSuper(methodName) {
    var fn = this.constructor.superclass.prototype[methodName];
    return (arguments.length > 1)
      ? fn.apply(this, slice.call(arguments, 1))
      : fn.call(this);
  }

  /**
   * Helper for creation of "classes".
   * @memberOf fabric.util
   * @param {Function} [parent] optional "Class" to inherit from
   * @param {Object} [properties] Properties shared by all instances of this class
   *                  (be careful modifying objects defined here as this would affect all instances)
   */
  function createClass() {
    var parent = null,
        properties = slice.call(arguments, 0);

    if (typeof properties[0] === 'function') {
      parent = properties.shift();
    }
    function klass() {
      this.initialize.apply(this, arguments);
    }

    klass.superclass = parent;
    klass.subclasses = [ ];

    if (parent) {
      Subclass.prototype = parent.prototype;
      klass.prototype = new Subclass();
      parent.subclasses.push(klass);
    }
    for (var i = 0, length = properties.length; i < length; i++) {
      addMethods(klass, properties[i], parent);
    }
    if (!klass.prototype.initialize) {
      klass.prototype.initialize = emptyFunction;
    }
    klass.prototype.constructor = klass;
    klass.prototype.callSuper = callSuper;
    return klass;
  }

  fabric.util.createClass = createClass;
})();