tools: enable no-var ESLint rule for lib

PR-URL: https://github.com/nodejs/node/pull/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>

.eslintrc.js

@@ -260,6 +260,7 @@ module.exports = {
     'no-useless-concat': 'error',
     'no-useless-constructor': 'error',
     'no-useless-return': 'error',
+    'no-var': 'error',
     'no-void': 'error',
     'no-whitespace-before-property': 'error',
     'object-curly-newline': 'error',

benchmark/.eslintrc.yaml

@@ -5,5 +5,4 @@ env:
   es6: true
 
 rules:
-  no-var: error
   prefer-arrow-callback: error

doc/.eslintrc.yaml

@@ -9,7 +9,6 @@ rules:
   symbol-description: off
 
   # Add new ECMAScript features gradually
-  no-var: error
   prefer-const: error
   prefer-rest-params: error
   prefer-template: error

lib/internal/async_hooks.js

@@ -196,6 +196,7 @@ function emitInitNative(asyncId, type, triggerAsyncId, resource) {
   try {
     // Using var here instead of let because "for (var ...)" is faster than let.
     // Refs: https://github.com/nodejs/node/pull/30380#issuecomment-552948364
+    // eslint-disable-next-line no-var
     for (var i = 0; i < active_hooks.array.length; i++) {
       if (typeof active_hooks.array[i][init_symbol] === 'function') {
         active_hooks.array[i][init_symbol](
@@ -228,6 +229,7 @@ function emitHook(symbol, asyncId) {
   try {
     // Using var here instead of let because "for (var ...)" is faster than let.
     // Refs: https://github.com/nodejs/node/pull/30380#issuecomment-552948364
+    // eslint-disable-next-line no-var
     for (var i = 0; i < active_hooks.array.length; i++) {
       if (typeof active_hooks.array[i][symbol] === 'function') {
         active_hooks.array[i][symbol](asyncId);

lib/internal/js_stream_socket.js

@@ -171,6 +171,7 @@ class JSStreamSocket extends Socket {
 
     this.stream.cork();
     // Use `var` over `let` for performance optimization.
+    // eslint-disable-next-line no-var
     for (var i = 0; i < bufs.length; ++i)
       this.stream.write(bufs[i], done);
     this.stream.uncork();

test/.eslintrc.yaml

@@ -6,7 +6,6 @@ env:
 
 rules:
   multiline-comment-style: [error, separate-lines]
-  no-var: error
   prefer-const: error
   symbol-description: off
 

tools/.eslintrc.yaml

@@ -12,4 +12,3 @@ rules:
     - error
     - args: after-used
   prefer-arrow-callback: error
-  no-var: error