Merge remote-tracking branch 'upstream/forward-dispatch'

* upstream/forward-dispatch:
  fix: forward dispatch return value
  Refactor example documentation structure and add CacheableLookup example (nodejs#3363)

Author: ronag

lib/dispatcher/dispatcher.js

@@ -39,18 +39,35 @@ class Dispatcher extends EventEmitter {
   }
 }
 
+const kOnDrain = Symbol('onDrain')
+const kOnConnect = Symbol('onConnect')
+const kOnDisconnect = Symbol('onDisconnect')
+const kOnConnectionError = Symbol('onConnectionError')
+
 class ComposedDispatcher extends Dispatcher {
-  #dispatcher = null
-  #dispatch = null
+  #dispatcher
+  #dispatch
 
   constructor (dispatcher, dispatch) {
     super()
+
     this.#dispatcher = dispatcher
     this.#dispatch = dispatch
+
+    this[kOnDrain] = (...args) => this.emit('drain', ...args)
+    this[kOnConnect] = (...args) => this.emit('connect', ...args)
+    this[kOnDisconnect] = (...args) => this.emit('disconnect', ...args)
+    this[kOnConnectionError] = (...args) => this.emit('connectionError', ...args)
+
+    this.#dispatcher
+      .on('drain', this[kOnDrain])
+      .on('connect', this[kOnConnect])
+      .on('disconnect', this[kOnDisconnect])
+      .on('connectionError', this[kOnConnectionError])
   }
 
   dispatch (...args) {
-    this.#dispatch(...args)
+    return this.#dispatch(...args)
   }
 
   close (...args) {