lib: prepare files for no-var lint rule

PR-URL: #42573
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Mohammed Keyvanzadeh <mohammadkeyvanzade94@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Akhil Marsonya <akhil.marsonya27@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

lib/internal/crypto/util.js

@@ -71,7 +71,7 @@ function lazyRequire(name) {
   return ret;
 }
 
-var defaultEncoding = 'buffer';
+let defaultEncoding = 'buffer';
 
 function setDefaultEncoding(val) {
   defaultEncoding = val;

lib/internal/dns/promises.js

@@ -67,7 +67,7 @@ function onlookupall(err, addresses) {
 
   const family = this.family;
 
-  for (var i = 0; i < addresses.length; i++) {
+  for (let i = 0; i < addresses.length; i++) {
     const address = addresses[i];
 
     addresses[i] = {
@@ -121,10 +121,10 @@ function createLookupPromise(family, hostname, all, hints, verbatim) {
 }
 
 function lookup(hostname, options) {
-  var hints = 0;
-  var family = -1;
-  var all = false;
-  var verbatim = getDefaultVerbatim();
+  let hints = 0;
+  let family = -1;
+  let all = false;
+  let verbatim = getDefaultVerbatim();
 
   // Parse arguments
   if (hostname) {
@@ -297,7 +297,7 @@ Resolver.prototype.resolveNaptr = resolveMap.NAPTR = resolver('queryNaptr');
 Resolver.prototype.resolveSoa = resolveMap.SOA = resolver('querySoa');
 Resolver.prototype.reverse = resolver('getHostByAddr');
 Resolver.prototype.resolve = function resolve(hostname, rrtype) {
-  var resolver;
+  let resolver;
 
   if (rrtype !== undefined) {
     validateString(rrtype, 'rrtype');

lib/internal/http2/util.js

@@ -588,7 +588,7 @@ const assertWithinRange = hideStackFrames(
 
 function toHeaderObject(headers, sensitiveHeaders) {
   const obj = ObjectCreate(null);
-  for (var n = 0; n < headers.length; n += 2) {
+  for (let n = 0; n < headers.length; n += 2) {
     const name = headers[n];
     let value = headers[n + 1];
     if (name === HTTP2_HEADER_STATUS)