Array.prototype.contains = function(pattern) {
        return this.indexOf(pattern) > -1;
};
 
EventDispatcher = function(/* dispatcher */) {
        var _listeners = [];
        var _dispatcher = arguments[0] || this;
 
        this.bindListener = function(event, listener) {
                if(!(listener instanceof Object)) {
                        return;
                }
                if(!_listeners[event]) {
                        _listeners[event] = [];
                }
                _listeners[event].push(listener);
        };
 
        this.unbindListener = function(event, listener) {
                if(_listeners[event] && _listeners[event].contains(listener)) {
                        _listeners[event].remove(listener);
                }
        };
 
        this.dispatchEvent = function(event) {
                if(!_listeners[event]) {
                        return;
                }
                for(var i = 0, length = this.listeners[event].length; i < length; i++) {
                        if(_listeners[event][i] instanceof Function) {
                                _listeners[event][i](event, _dispatcher);
                        }
                }
        };
};
 
/* пример использования */
Step = function(options) {
 
        this.eventDispatcher = new EventDispatcher(this);
 
        this.bindListener = function(event, listener) {
                this.eventDispatcher.bindListener(event, listener);
        };
 
        this.unbindListener = function(event, listener) {
                this.eventDispatcher.unbindListener(event, listener);
        };
 
        this.setValue = function(value) {
                this._value = value;
                this.eventDispatcher.dispatchEvent(Step.EVENT_SET_VALUE);
        };
};
calc.Step.EVENT_SET_VALUE = 'setvalue';