util: improve debuglog performance

PR-URL: #28956
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

lib/internal/util/debuglog.js

@@ -33,7 +33,7 @@ function emitWarningIfNeeded(set) {
 
 function debuglogImpl(set) {
   set = set.toUpperCase();
-  if (!debugs[set]) {
+  if (debugs[set] === undefined) {
     if (debugEnvRegex.test(set)) {
       const pid = process.pid;
       emitWarningIfNeeded(set);
@@ -42,7 +42,7 @@ function debuglogImpl(set) {
         process.stderr.write(format('%s %d: %s\n', set, pid, msg));
       };
     } else {
-      debugs[set] = function debug() {};
+      debugs[set] = null;
     }
   }
   return debugs[set];
@@ -55,12 +55,13 @@ function debuglogImpl(set) {
 function debuglog(set) {
   let debug;
   return function(...args) {
-    if (!debug) {
+    if (debug === undefined) {
       // Only invokes debuglogImpl() when the debug function is
       // called for the first time.
       debug = debuglogImpl(set);
     }
-    debug(...args);
+    if (debug !== null)
+      debug(...args);
   };
 }