src: lib/internal/timers.js var -> let/const

PR-URL: #30314
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

lib/internal/timers.js

@@ -313,7 +313,7 @@ function insert(item, refed, start) {
   item._idleStart = start;
 
   // Use an existing list if there is one, otherwise we need to make a new one.
-  var list = timerListMap[msecs];
+  let list = timerListMap[msecs];
   if (list === undefined) {
     debug('no %d list was found in insert, creating a new one', msecs);
     const expiry = start + msecs;
@@ -396,7 +396,7 @@ function getTimerCallbacks(runNextTicks) {
   function processImmediate() {
     const queue = outstandingQueue.head !== null ?
       outstandingQueue : immediateQueue;
-    var immediate = queue.head;
+    let immediate = queue.head;
 
     // Clear the linked list early in case new `setImmediate()`
     // calls occur while immediate callbacks are executed
@@ -482,10 +482,10 @@ function getTimerCallbacks(runNextTicks) {
 
     debug('timeout callback %d', msecs);
 
-    var diff, timer;
     let ranAtLeastOneTimer = false;
+    let timer;
     while (timer = L.peek(list)) {
-      diff = now - timer._idleStart;
+      const diff = now - timer._idleStart;
 
       // Check if this loop iteration is too early for the next timer.
       // This happens if there are more timers scheduled for later in the list.