process: clean up signal handler setup

PR-URL: nodejs#18330
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>

lib/internal/process.js

@@ -178,24 +178,23 @@ function setupKillAndExit() {
 
 
 function setupSignalHandlers() {
-  // Load events module in order to access prototype elements on process like
-  // process.addListener.
-  const signalWraps = {};
+  const signalWraps = Object.create(null);
+  let Signal;
 
   function isSignal(event) {
     return typeof event === 'string' && constants[event] !== undefined;
   }
 
   // Detect presence of a listener for the special signal types
-  process.on('newListener', function(type, listener) {
-    if (isSignal(type) &&
-        !signalWraps.hasOwnProperty(type)) {
-      const Signal = process.binding('signal_wrap').Signal;
+  process.on('newListener', function(type) {
+    if (isSignal(type) && signalWraps[type] === undefined) {
+      if (Signal === undefined)
+        Signal = process.binding('signal_wrap').Signal;
       const wrap = new Signal();
 
       wrap.unref();
 
-      wrap.onsignal = function() { process.emit(type, type); };
+      wrap.onsignal = process.emit.bind(process, type, type);
 
       const signum = constants[type];
       const err = wrap.start(signum);
@@ -208,8 +207,8 @@ function setupSignalHandlers() {
     }
   });
 
-  process.on('removeListener', function(type, listener) {
-    if (signalWraps.hasOwnProperty(type) && this.listenerCount(type) === 0) {
+  process.on('removeListener', function(type) {
+    if (signalWraps[type] !== undefined && this.listenerCount(type) === 0) {
       signalWraps[type].close();
       delete signalWraps[type];
     }