process: replace var with let/const

PR-URL: https://github.com/nodejs/node/pull/30382
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

lib/internal/process/stdio.js

@@ -19,9 +19,9 @@ function dummyDestroy(err, cb) {
 }
 
 function getMainThreadStdio() {
-  var stdin;
-  var stdout;
-  var stderr;
+  let stdin;
+  let stdout;
+  let stderr;
 
   function getStdout() {
     if (stdout) return stdout;
@@ -53,7 +53,7 @@ function getMainThreadStdio() {
 
     switch (guessHandleType(fd)) {
       case 'TTY':
-        var tty = require('tty');
+        const tty = require('tty');
         stdin = new tty.ReadStream(fd, {
           highWaterMark: 0,
           readable: true,
@@ -62,13 +62,13 @@ function getMainThreadStdio() {
         break;
 
       case 'FILE':
-        var fs = require('fs');
+        const fs = require('fs');
         stdin = new fs.ReadStream(null, { fd: fd, autoClose: false });
         break;
 
       case 'PIPE':
       case 'TCP':
-        var net = require('net');
+        const net = require('net');
 
         // It could be that process has been started with an IPC channel
         // sitting on fd=0, in such case the pipe for this fd is already
@@ -147,11 +147,11 @@ function getMainThreadStdio() {
 }
 
 function createWritableStdioStream(fd) {
-  var stream;
+  let stream;
   // Note stream._type is used for test-module-load-list.js
   switch (guessHandleType(fd)) {
     case 'TTY':
-      var tty = require('tty');
+      const tty = require('tty');
       stream = new tty.WriteStream(fd);
       stream._type = 'tty';
       break;
@@ -164,7 +164,7 @@ function createWritableStdioStream(fd) {
 
     case 'PIPE':
     case 'TCP':
-      var net = require('net');
+      const net = require('net');
 
       // If fd is already being used for the IPC channel, libuv will return
       // an error when trying to use it again. In that case, create the socket