http: revise _http_server.js

* replace var with const
* eliminate unnecessary bytesParsed variable

http: remove bytesParsed var

PR-URL: #30279
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Yorkie Liu <yorkiefixer@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_http_server.js

@@ -253,13 +253,13 @@ function writeHead(statusCode, reason, obj) {
   }
   this.statusCode = statusCode;
 
-  var headers;
+  let headers;
   if (this[kOutHeaders]) {
     // Slow-case: when progressive API and header fields are passed.
-    var k;
+    let k;
     if (obj) {
-      var keys = Object.keys(obj);
-      for (var i = 0; i < keys.length; i++) {
+      const keys = Object.keys(obj);
+      for (let i = 0; i < keys.length; i++) {
         k = keys[i];
         if (k) this.setHeader(k, obj[k]);
       }
@@ -487,7 +487,7 @@ function socketOnClose(socket, state) {
 
 function abortIncoming(incoming) {
   while (incoming.length) {
-    var req = incoming.shift();
+    const req = incoming.shift();
     req.aborted = true;
     req.emit('aborted');
     req.emit('close');
@@ -577,8 +577,7 @@ function onParserExecuteCommon(server, socket, parser, state, ret, d) {
     socketOnError.call(socket, ret);
   } else if (parser.incoming && parser.incoming.upgrade) {
     // Upgrade or CONNECT
-    var bytesParsed = ret;
-    var req = parser.incoming;
+    const req = parser.incoming;
     debug('SERVER upgrade or connect', req.method);
 
     if (!d)
@@ -594,10 +593,10 @@ function onParserExecuteCommon(server, socket, parser, state, ret, d) {
     freeParser(parser, req, socket);
     parser = null;
 
-    var eventName = req.method === 'CONNECT' ? 'connect' : 'upgrade';
+    const eventName = req.method === 'CONNECT' ? 'connect' : 'upgrade';
     if (eventName === 'upgrade' || server.listenerCount(eventName) > 0) {
       debug('SERVER have listener for %s', eventName);
-      var bodyHead = d.slice(bytesParsed, d.length);
+      const bodyHead = d.slice(ret, d.length);
 
       socket.readableFlowing = null;
       server.emit(eventName, req, socket, bodyHead);
@@ -659,7 +658,7 @@ function resOnFinish(req, res, socket, state, server) {
     }
   } else {
     // Start sending the next message
-    var m = state.outgoing.shift();
+    const m = state.outgoing.shift();
     if (m) {
       m.assignSocket(socket);
     }
@@ -696,7 +695,7 @@ function parserOnIncoming(server, socket, state, req, keepAlive) {
   // so that we don't become overwhelmed by a flood of
   // pipelined requests that may never be resolved.
   if (!socket._paused) {
-    var ws = socket._writableState;
+    const ws = socket._writableState;
     if (ws.needDrain || state.outgoingData >= socket.writableHighWaterMark) {
       socket._paused = true;
       // We also need to pause the parser, but don't do that until after