benchmark: replace deprecated and eliminate var in buffer-from.js

PR-URL: https://github.com/nodejs/node/pull/26585
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

benchmark/buffers/buffer-from.js

@@ -26,19 +26,17 @@ function main({ len, n, source }) {
   const uint8array = new Uint8Array(len);
   const obj = { length: null }; // Results in a new, empty Buffer
 
-  var i;
-
   switch (source) {
     case 'array':
       bench.start();
-      for (i = 0; i < n * 1024; i++) {
+      for (let i = 0; i < n * 1024; i++) {
         Buffer.from(array);
       }
       bench.end(n);
       break;
     case 'arraybuffer':
       bench.start();
-      for (i = 0; i < n * 1024; i++) {
+      for (let i = 0; i < n * 1024; i++) {
         Buffer.from(arrayBuf);
       }
       bench.end(n);
@@ -47,54 +45,54 @@ function main({ len, n, source }) {
       const offset = ~~(len / 4);
       const length = ~~(len / 2);
       bench.start();
-      for (i = 0; i < n * 1024; i++) {
+      for (let i = 0; i < n * 1024; i++) {
         Buffer.from(arrayBuf, offset, length);
       }
       bench.end(n);
       break;
     case 'buffer':
       bench.start();
-      for (i = 0; i < n * 1024; i++) {
+      for (let i = 0; i < n * 1024; i++) {
         Buffer.from(buffer);
       }
       bench.end(n);
       break;
     case 'uint8array':
       bench.start();
-      for (i = 0; i < n * 1024; i++) {
+      for (let i = 0; i < n * 1024; i++) {
         Buffer.from(uint8array);
       }
       bench.end(n);
       break;
     case 'string':
       bench.start();
-      for (i = 0; i < n * 1024; i++) {
+      for (let i = 0; i < n * 1024; i++) {
         Buffer.from(str);
       }
       bench.end(n);
       break;
     case 'string-utf8':
       bench.start();
-      for (i = 0; i < n * 1024; i++) {
+      for (let i = 0; i < n * 1024; i++) {
         Buffer.from(str, 'utf8');
       }
       bench.end(n);
       break;
     case 'string-base64':
       bench.start();
-      for (i = 0; i < n * 1024; i++) {
+      for (let i = 0; i < n * 1024; i++) {
         Buffer.from(str, 'base64');
       }
       bench.end(n);
       break;
     case 'object':
       bench.start();
-      for (i = 0; i < n * 1024; i++) {
+      for (let i = 0; i < n * 1024; i++) {
         Buffer.from(obj);
       }
       bench.end(n);
       break;
     default:
-      assert.fail(null, null, 'Should not get here');
+      assert.fail('Should not get here');
   }
 }