Server#close takes a callback function.

socket.io/index.d.ts

@@ -180,7 +180,7 @@ declare namespace SocketIO {
 		/**
 		 * Closes the server connection
 		 */
-		close():void;
+		close( fn ?: () => void ):void;
 
 		/**
 		 * The event fired when we get a new connection

socket.io/socket.io-tests.ts

@@ -143,3 +143,14 @@ function testUsingItJustAsACrossBrowserWebSocket() {
         socket.on('disconnect', function () { });
     });
 }
+
+function testClosingServerWithCallback() {
+    var io = socketIO.listen(80);
+    io.close(function() {
+    });
+}
+
+function testClosingServerWithoutCallback() {
+    var io = socketIO.listen(80);
+    io.close();
+}