allow a message hook to also be an object

src/core/messaging.ts

@@ -174,21 +174,14 @@ interface IMessageHandler {
 
 
 /**
- * A function which intercepts messages sent to a message handler.
- *
- * @param handler - The target handler of the message.
- *
- * @param msg - The message to be sent to the handler.
- *
- * @returns `true` if the message should continue to be processed
- *   as normal, or `false` if processing should cease immediately.
+ * An object which intercepts messages sent to a message handler.
  *
  * #### Notes
  * A message hook is useful for intercepting or spying on messages
  * sent to message handlers which were either not created by the
  * consumer, or when subclassing the handler is not feasible.
  *
- * If the function returns `false`, no other message hooks will be
+ * If `messageHook` returns `false`, no other message hooks will be
  * invoked and the message will not be delivered to the handler.
  *
  * If all installed message hooks return `true`, the message will
@@ -197,7 +190,30 @@ interface IMessageHandler {
  * **See also:** [[installMessageHook]] and [[removeMessageHook]]
  */
 export
-type MessageHook = (handler: IMessageHandler, msg: Message) => boolean;
+interface IMessageHook {
+  /**
+   * Intercept a message sent to a message handler.
+   *
+   * @param handler - The target handler of the message.
+   *
+   * @param msg - The message to be sent to the handler.
+   *
+   * @returns `true` if the message should continue to be processed
+   *   as normal, or `false` if processing should cease immediately.
+   */
+  messageHook(handler: IMessageHandler, msg: Message): boolean;
+}
+
+
+/**
+ * A type alias for message hook object or function.
+ *
+ * #### Notes
+ * The signature and semantics of a message hook function are the same
+ * as the `messageHook` method of [[IMessageHook]].
+ */
+export
+type MessageHook = IMessageHook | ((handler: IMessageHandler, msg: Message) => boolean);
 
 
 /**
@@ -471,7 +487,11 @@ namespace MessageLoop {
   function invokeHook(hook: MessageHook, handler: IMessageHandler, msg: Message): boolean {
     let result: boolean;
     try {
-      result = hook(handler, msg);
+      if (typeof hook === 'function') {
+        result = hook(handler, msg);
+      } else {
+        result = hook.messageHook(handler, msg);
+      }
     } catch (err) {
       result = true;
       console.error(err);