diff --git a/test/parallel/test-debug-brk.js b/test/parallel/test-debug-brk.js
index 49b19898e030b9..b833421f93c15f 100644
--- a/test/parallel/test-debug-brk.js
+++ b/test/parallel/test-debug-brk.js
@@ -4,6 +4,6 @@ const common = require('../common');
 const assert = require('assert');
 const spawnSync = require('child_process').spawnSync;
 
-const args = [`--debug-brk=${common.PORT}`, `-e`, `0`];
+const args = [`--debug-brk=${common.PORT}`, '-e', '0'];
 const proc = spawnSync(process.execPath, args, {encoding: 'utf8'});
 assert(/Debugger listening on/.test(proc.stderr));
diff --git a/test/parallel/test-debug-no-context.js b/test/parallel/test-debug-no-context.js
index 11a9aa17150bbb..649a7b9b06504c 100644
--- a/test/parallel/test-debug-no-context.js
+++ b/test/parallel/test-debug-no-context.js
@@ -4,7 +4,7 @@ const common = require('../common');
 const assert = require('assert');
 const spawn = require('child_process').spawn;
 
-const args = [`--debug`, `--debug-port=${common.PORT}`, `--interactive`];
+const args = ['--debug', `--debug-port=${common.PORT}`, '--interactive'];
 const proc = spawn(process.execPath, args, { stdio: 'pipe' });
 proc.stdin.write(`
     util.inspect(Promise.resolve(42));
diff --git a/test/parallel/test-dgram-udp4.js b/test/parallel/test-dgram-udp4.js
index e845c5d845549c..b36034f75dd2cf 100644
--- a/test/parallel/test-dgram-udp4.js
+++ b/test/parallel/test-dgram-udp4.js
@@ -4,10 +4,10 @@ const assert = require('assert');
 const dgram = require('dgram');
 const server_port = common.PORT;
 const message_to_send = 'A message to send';
-let server, client;
+let client;
 let timer;
 
-server = dgram.createSocket('udp4');
+const server = dgram.createSocket('udp4');
 server.on('message', function(msg, rinfo) {
   console.log('server got: ' + msg +
               ' from ' + rinfo.address + ':' + rinfo.port);
diff --git a/test/parallel/test-file-write-stream3.js b/test/parallel/test-file-write-stream3.js
index 07afeab48310d7..72f869ecf78559 100644
--- a/test/parallel/test-file-write-stream3.js
+++ b/test/parallel/test-file-write-stream3.js
@@ -126,7 +126,6 @@ function run_test_3() {
   var file, options;
 
   const data = '\u2026\u2026';    // 3 bytes * 2 = 6 bytes in UTF-8
-  let fileData;
 
   options = { start: 10,
               flags: 'r+' };
@@ -144,7 +143,7 @@ function run_test_3() {
     console.log('    (debug: start         ', file.start);
     console.log('    (debug: pos           ', file.pos);
     assert.strictEqual(file.bytesWritten, data.length * 3);
-    fileData = fs.readFileSync(filepath, 'utf8');
+    const fileData = fs.readFileSync(filepath, 'utf8');
     console.log('    (debug: file data   ', fileData);
     console.log('    (debug: expected    ', fileDataExpected_3);
     assert.equal(fileData, fileDataExpected_3);
diff --git a/test/parallel/test-fs-realpath.js b/test/parallel/test-fs-realpath.js
index b18afac12d4a78..dcc28ce4d99afa 100644
--- a/test/parallel/test-fs-realpath.js
+++ b/test/parallel/test-fs-realpath.js
@@ -90,7 +90,7 @@ function test_simple_relative_symlink(callback) {
   [
     [entry, '../' + common.tmpDirName + '/cycles/root.js']
   ].forEach(function(t) {
-    try {fs.unlinkSync(t[0]);}catch (e) {}
+    try {fs.unlinkSync(t[0]);} catch (e) {}
     console.log('fs.symlinkSync(%j, %j, %j)', t[1], t[0], 'file');
     fs.symlinkSync(t[1], t[0], 'file');
     unlink.push(t[0]);
diff --git a/test/parallel/test-path.js b/test/parallel/test-path.js
index 8b528cf2afee34..aeb6ec0c49bbf7 100644
--- a/test/parallel/test-path.js
+++ b/test/parallel/test-path.js
@@ -316,12 +316,11 @@ joinTests.forEach(function(test) {
     test[1].forEach(function(test) {
       const actual = join.apply(null, test[0]);
       const expected = test[1];
-      let actualAlt;
       // For non-Windows specific tests with the Windows join(), we need to try
       // replacing the slashes since the non-Windows specific tests' `expected`
       // use forward slashes
-      if (join === path.win32.join)
-        actualAlt = actual.replace(/\\/g, '/');
+      const actualAlt = (join === path.win32.join) ?
+        actual.replace(/\\/g, '/') : undefined;
       const fn = 'path.' +
                  (join === path.win32.join ? 'win32' : 'posix') +
                  '.join(';
diff --git a/test/parallel/test-tls-two-cas-one-string.js b/test/parallel/test-tls-two-cas-one-string.js
index c3b5d6961c11c4..ba9b3609c2653d 100644
--- a/test/parallel/test-tls-two-cas-one-string.js
+++ b/test/parallel/test-tls-two-cas-one-string.js
@@ -5,13 +5,13 @@ const tls = require('tls');
 const fs = require('fs');
 
 const ca1 =
-    fs.readFileSync(`${common.fixturesDir}/keys/ca1-cert.pem`, `utf8`);
+    fs.readFileSync(`${common.fixturesDir}/keys/ca1-cert.pem`, 'utf8');
 const ca2 =
-    fs.readFileSync(`${common.fixturesDir}/keys/ca2-cert.pem`, `utf8`);
+    fs.readFileSync(`${common.fixturesDir}/keys/ca2-cert.pem`, 'utf8');
 const cert =
-    fs.readFileSync(`${common.fixturesDir}/keys/agent3-cert.pem`, `utf8`);
+    fs.readFileSync(`${common.fixturesDir}/keys/agent3-cert.pem`, 'utf8');
 const key =
-    fs.readFileSync(`${common.fixturesDir}/keys/agent3-key.pem`, `utf8`);
+    fs.readFileSync(`${common.fixturesDir}/keys/agent3-key.pem`, 'utf8');
 
 function test(ca, next) {
   const server = tls.createServer({ ca, cert, key }, function(conn) {
diff --git a/test/parallel/test-url.js b/test/parallel/test-url.js
index 95bde7b861e668..9aa2682cbcb523 100644
--- a/test/parallel/test-url.js
+++ b/test/parallel/test-url.js
@@ -259,20 +259,19 @@ var parseTests = {
     path: '/vt/lyrs=m@114???&hl=en&src=api&x=2&y=2&z=3&s='
   },
 
-  'http://user:pass@mt0.google.com/vt/lyrs=m@114???&hl=en&src=api&x=2&y=2&z=3&s=':
-    {
-      href: 'http://user:pass@mt0.google.com/vt/lyrs=m@114???' +
-            '&hl=en&src=api&x=2&y=2&z=3&s=',
-      protocol: 'http:',
-      slashes: true,
-      host: 'mt0.google.com',
-      auth: 'user:pass',
-      hostname: 'mt0.google.com',
-      search: '???&hl=en&src=api&x=2&y=2&z=3&s=',
-      query: '??&hl=en&src=api&x=2&y=2&z=3&s=',
-      pathname: '/vt/lyrs=m@114',
-      path: '/vt/lyrs=m@114???&hl=en&src=api&x=2&y=2&z=3&s='
-    },
+  'http://user:pass@mt0.google.com/vt/lyrs=m@114???&hl=en&src=api&x=2&y=2&z=3&s=': {
+    href: 'http://user:pass@mt0.google.com/vt/lyrs=m@114???' +
+          '&hl=en&src=api&x=2&y=2&z=3&s=',
+    protocol: 'http:',
+    slashes: true,
+    host: 'mt0.google.com',
+    auth: 'user:pass',
+    hostname: 'mt0.google.com',
+    search: '???&hl=en&src=api&x=2&y=2&z=3&s=',
+    query: '??&hl=en&src=api&x=2&y=2&z=3&s=',
+    pathname: '/vt/lyrs=m@114',
+    path: '/vt/lyrs=m@114???&hl=en&src=api&x=2&y=2&z=3&s='
+  },
 
   'file:///etc/passwd': {
     href: 'file:///etc/passwd',
diff --git a/test/sequential/test-child-process-fork-getconnections.js b/test/sequential/test-child-process-fork-getconnections.js
index f7bb9f5eea216f..8928ef6c744ba4 100644
--- a/test/sequential/test-child-process-fork-getconnections.js
+++ b/test/sequential/test-child-process-fork-getconnections.js
@@ -56,9 +56,9 @@ if (process.argv[2] === 'child') {
 
   let disconnected = 0;
   server.on('listening', function() {
-    let j = count, client;
+    let j = count;
     while (j--) {
-      client = net.connect(common.PORT, '127.0.0.1');
+      const client = net.connect(common.PORT, '127.0.0.1');
       client.on('close', function() {
         disconnected += 1;
       });
diff --git a/tools/doc/addon-verify.js b/tools/doc/addon-verify.js
index 792fd69eabf027..5fe6f093d53d1b 100644
--- a/tools/doc/addon-verify.js
+++ b/tools/doc/addon-verify.js
@@ -12,7 +12,6 @@ const contents = fs.readFileSync(doc).toString();
 
 const tokens = marked.lexer(contents, {});
 let files = null;
-let blockName;
 let id = 0;
 
 // Just to make sure that all examples will be processed
@@ -28,7 +27,7 @@ oldDirs = oldDirs.filter(function(dir) {
 for (var i = 0; i < tokens.length; i++) {
   var token = tokens[i];
   if (token.type === 'heading' && token.text) {
-    blockName = token.text;
+    const blockName = token.text;
     if (files && Object.keys(files).length !== 0) {
       verifyFiles(files,
                   blockName,