improvement: Micro-optimize the runHandler() function

lib/RequestHandlers.js

@@ -47,20 +47,24 @@ function runOnFinishedHooks() {
 }
 
 function runHandler(res) {
-  var result = res._route.handler(res.request, res)
+  const result = res._route.handler(res.request, res)
+
   if (result && typeof result.then === 'function') {
-    result
-      .then((payload) => {
-        if (payload !== undefined) {
-          res.send(payload)
-        }
-      }, (err) => {
-        if (res.sent) {
-          throw err // Re-throw the error since it is a system error
-        }
-        runOnErrorHooks(err, res)
-      })
+    result.then(onHandlerResolve.bind(res), onHandlerReject.bind(res))
+  }
+}
+
+function onHandlerResolve(body) {
+  if (body !== undefined) {
+    this.send(body)
+  }
+}
+
+function onHandlerReject(err) {
+  if (this.sent) {
+    throw err // Re-throw the error since it is a system error
   }
+  runOnErrorHooks(err, this)
 }
 
 function createOptionsHandler(allowedMethods) {