scope.$on is not a function

I have a one error:
scope.$on is not a function
at http://URL/js/socket/directive.socket.js:92:21

`forward: function (events, scope) {
if (events instanceof Array === false) {
events = [events];
}
if (!scope) {
scope = defaultScope;
}
events.forEach(function (eventName) {
var prefixedEvent = prefix + eventName;
var forwardBroadcast = asyncAngularify(socket, function () {
Array.prototype.unshift.call(arguments, prefixedEvent);
scope.$broadcast.apply(scope, arguments);
});
**scope.$on**('$destroy', function () {
socket.removeListener(eventName, forwardBroadcast);
});
socket.on(eventName, forwardBroadcast);
});
}`