stream: change var to let/const in stream files

PR-URL: #32214
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/_stream_readable.js

@@ -444,7 +444,7 @@ Readable.prototype.read = function(n) {
   // 3. Actually pull the requested chunks out of the buffer and return.
 
   // if we need a readable event, then we need to do some reading.
-  var doRead = state.needReadable;
+  let doRead = state.needReadable;
   debug('need readable', doRead);
 
   // If we currently have less than the highWaterMark, then also read some
@@ -475,7 +475,7 @@ Readable.prototype.read = function(n) {
       n = howMuchToRead(nOrig, state);
   }
 
-  var ret;
+  let ret;
   if (n > 0)
     ret = fromList(n, state);
   else
@@ -514,7 +514,7 @@ function onEofChunk(stream, state) {
   debug('onEofChunk');
   if (state.ended) return;
   if (state.decoder) {
-    var chunk = state.decoder.end();
+    const chunk = state.decoder.end();
     if (chunk && chunk.length) {
       state.buffer.push(chunk);
       state.length += state.objectMode ? 1 : chunk.length;
@@ -675,7 +675,7 @@ Readable.prototype.pipe = function(dest, pipeOpts) {
 
   let ondrain;
 
-  var cleanedUp = false;
+  let cleanedUp = false;
   function cleanup() {
     debug('cleanup');
     // Cleanup event handlers once the pipe is broken
@@ -816,7 +816,7 @@ Readable.prototype.unpipe = function(dest) {
 
   if (!dest) {
     // remove all.
-    var dests = state.pipes;
+    const dests = state.pipes;
     state.pipes = [];
     this.pause();
 
@@ -984,12 +984,12 @@ function flow(stream) {
 // It is an ugly unfortunate mess of history.
 Readable.prototype.wrap = function(stream) {
   const state = this._readableState;
-  var paused = false;
+  let paused = false;
 
   stream.on('end', () => {
     debug('wrapped end');
     if (state.decoder && !state.ended) {
-      var chunk = state.decoder.end();
+      const chunk = state.decoder.end();
       if (chunk && chunk.length)
         this.push(chunk);
     }
@@ -1161,7 +1161,7 @@ function fromList(n, state) {
   if (state.length === 0)
     return null;
 
-  var ret;
+  let ret;
   if (state.objectMode)
     ret = state.buffer.shift();
   else if (!n || n >= state.length) {

lib/_stream_transform.js

@@ -172,7 +172,7 @@ Transform.prototype._write = function(chunk, encoding, cb) {
   ts.writechunk = chunk;
   ts.writeencoding = encoding;
   if (!ts.transforming) {
-    var rs = this._readableState;
+    const rs = this._readableState;
     if (ts.needTransform ||
         rs.needReadable ||
         rs.length < rs.highWaterMark)