zlib: name every function Ref: #8913

PR-URL: https://github.com/nodejs/node/pull/9389
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

lib/zlib.js

@@ -346,7 +346,7 @@ function Zlib(opts, mode) {
 
   var self = this;
   this._hadError = false;
-  this._handle.onerror = function(message, errno) {
+  this._handle.onerror = function onErrorHandler(message, errno) {
     // there is no way to cleanly recover.
     // continuing only obscures problems.
     _close(self);
@@ -401,7 +401,7 @@ Zlib.prototype.params = function(level, strategy, callback) {
 
   if (this._level !== level || this._strategy !== strategy) {
     var self = this;
-    this.flush(constants.Z_SYNC_FLUSH, function() {
+    this.flush(constants.Z_SYNC_FLUSH, function flushCallback() {
       assert(self._handle, 'zlib binding closed');
       self._handle.params(level, strategy);
       if (!self._hadError) {
@@ -442,7 +442,8 @@ Zlib.prototype.flush = function(kind, callback) {
       this.once('end', callback);
   } else if (ws.needDrain) {
     if (callback) {
-      this.once('drain', () => this.flush(kind, callback));
+      const drainHandler = () => this.flush(kind, callback);
+      this.once('drain', drainHandler);
     }
   } else {
     this._flushFlag = kind;