tools: enable eslint no-undef-init rule

This also fixes the three entries that did not pass.

PR-URL: https://github.com/nodejs/node/pull/18831
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matheus Marchini <matheus@sthima.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

.eslintrc.js

@@ -130,6 +130,7 @@ module.exports = {
     // http://eslint.org/docs/rules/#variables
     'no-delete-var': 'error',
     'no-undef': 'error',
+    'no-undef-init': 'error',
     'no-unused-vars': ['error', { args: 'none' }],
     'no-use-before-define': ['error', {
       classes: true,

lib/internal/util.js

@@ -228,8 +228,8 @@ function getSystemErrorName(err) {
 // getConstructorOf is wrapped into this to save iterations
 function getIdentificationOf(obj) {
   const original = obj;
-  let constructor = undefined;
-  let tag = undefined;
+  let constructor;
+  let tag;
 
   while (obj) {
     if (constructor === undefined) {

test/parallel/test-fs-utimes.js

@@ -88,7 +88,7 @@ function testIt(atime, mtime, callback) {
       expect_errno('futimesSync', fd, ex, 'ENOSYS');
     }
 
-    let err = undefined;
+    let err;
     try {
       fs.utimesSync('foobarbaz', atime, mtime);
     } catch (ex) {