diff --git a/lib/_http_client.js b/lib/_http_client.js
index 4e5912608425b9..6436d22f6e6540 100644
--- a/lib/_http_client.js
+++ b/lib/_http_client.js
@@ -220,7 +220,7 @@ function ClientRequest(input, options, cb) {
       // https://tools.ietf.org/html/rfc3986#section-3.2.2
       var posColon = hostHeader.indexOf(':');
       if (posColon !== -1 &&
-          hostHeader.indexOf(':', posColon + 1) !== -1 &&
+          hostHeader.includes(':', posColon + 1) &&
           hostHeader.charCodeAt(0) !== 91/* '[' */) {
         hostHeader = `[${hostHeader}]`;
       }
diff --git a/lib/_stream_readable.js b/lib/_stream_readable.js
index fe77c441861478..ba948c61948b57 100644
--- a/lib/_stream_readable.js
+++ b/lib/_stream_readable.js
@@ -713,7 +713,7 @@ Readable.prototype.pipe = function(dest, pipeOpts) {
       // also returned false.
       // => Check whether `dest` is still a piping destination.
       if (((state.pipesCount === 1 && state.pipes === dest) ||
-           (state.pipesCount > 1 && state.pipes.indexOf(dest) !== -1)) &&
+           (state.pipesCount > 1 && state.pipes.includes(dest))) &&
           !cleanedUp) {
         debug('false write response, pause', state.awaitDrain);
         state.awaitDrain++;
diff --git a/lib/assert.js b/lib/assert.js
index 94e9406393bf67..e32cae3cffbc17 100644
--- a/lib/assert.js
+++ b/lib/assert.js
@@ -284,7 +284,7 @@ function getErrMessage(message, fn) {
     // Flush unfinished multi byte characters.
     decoder.end();
     // Always normalize indentation, otherwise the message could look weird.
-    if (message.indexOf('\n') !== -1) {
+    if (message.includes('\n')) {
       if (EOL === '\r\n') {
         message = message.replace(/\r\n/g, '\n');
       }
diff --git a/lib/child_process.js b/lib/child_process.js
index 8060412b3f076f..805600820f37c3 100644
--- a/lib/child_process.js
+++ b/lib/child_process.js
@@ -101,7 +101,7 @@ exports.fork = function fork(modulePath /* , args, options */) {
     // and stderr from the parent if silent isn't set.
     options.stdio = options.silent ? stdioStringToArray('pipe') :
       stdioStringToArray('inherit');
-  } else if (options.stdio.indexOf('ipc') === -1) {
+  } else if (!options.stdio.includes('ipc')) {
     throw new ERR_CHILD_PROCESS_IPC_REQUIRED('options.stdio');
   }
 
diff --git a/lib/internal/cluster/shared_handle.js b/lib/internal/cluster/shared_handle.js
index 408657623b2e3b..0d0a805709a010 100644
--- a/lib/internal/cluster/shared_handle.js
+++ b/lib/internal/cluster/shared_handle.js
@@ -24,7 +24,7 @@ function SharedHandle(key, address, port, addressType, fd, flags) {
 }
 
 SharedHandle.prototype.add = function(worker, send) {
-  assert(this.workers.indexOf(worker) === -1);
+  assert(!this.workers.includes(worker));
   this.workers.push(worker);
   send(this.errno, null, this.handle);
 };
diff --git a/lib/internal/console/constructor.js b/lib/internal/console/constructor.js
index 2fa812d9fe1bcc..b9af931d385b41 100644
--- a/lib/internal/console/constructor.js
+++ b/lib/internal/console/constructor.js
@@ -220,7 +220,7 @@ Console.prototype[kWriteToConsole] = function(streamSymbol, string) {
     this._stdoutErrorHandler : this._stderrErrorHandler;
 
   if (groupIndent.length !== 0) {
-    if (string.indexOf('\n') !== -1) {
+    if (string.includes('\n')) {
       string = string.replace(/\n/g, `\n${groupIndent}`);
     }
     string = groupIndent + string;
diff --git a/lib/internal/fs/utils.js b/lib/internal/fs/utils.js
index 8a9d4d357204ec..0c5ce1ecb76b91 100644
--- a/lib/internal/fs/utils.js
+++ b/lib/internal/fs/utils.js
@@ -191,8 +191,8 @@ function nullCheck(path, propName, throwError = true) {
 
   // We can only perform meaningful checks on strings and Uint8Arrays.
   if (!pathIsString && !pathIsUint8Array ||
-      pathIsString && path.indexOf('\u0000') === -1 ||
-      pathIsUint8Array && path.indexOf(0) === -1) {
+      pathIsString && !path.includes('\u0000') ||
+      pathIsUint8Array && !path.includes(0)) {
     return;
   }
 
diff --git a/lib/internal/util/inspect.js b/lib/internal/util/inspect.js
index 4cee2d8b9fb4a3..dc97e6dceb8c5a 100644
--- a/lib/internal/util/inspect.js
+++ b/lib/internal/util/inspect.js
@@ -288,12 +288,12 @@ function strEscape(str) {
   // instead wrap the text in double quotes. If double quotes exist, check for
   // backticks. If they do not exist, use those as fallback instead of the
   // double quotes.
-  if (str.indexOf("'") !== -1) {
+  if (str.includes("'")) {
     // This invalidates the charCode and therefore can not be matched for
     // anymore.
-    if (str.indexOf('"') === -1) {
+    if (!str.includes('"')) {
       singleQuote = -1;
-    } else if (str.indexOf('`') === -1 && str.indexOf('${') === -1) {
+    } else if (!str.includes('`') && !str.includes('${')) {
       singleQuote = -2;
     }
     if (singleQuote !== 39) {
@@ -557,7 +557,7 @@ function formatValue(ctx, value, recurseTimes, typedArray) {
 
   // Using an array here is actually better for the average case than using
   // a Set. `seen` will only check for the depth and will never grow too large.
-  if (ctx.seen.indexOf(value) !== -1)
+  if (ctx.seen.includes(value))
     return ctx.stylize('[Circular]', 'special');
 
   return formatRaw(ctx, value, recurseTimes, typedArray);
diff --git a/lib/url.js b/lib/url.js
index ff54988f424326..ade0007171ee48 100644
--- a/lib/url.js
+++ b/lib/url.js
@@ -581,9 +581,9 @@ Url.prototype.format = function format() {
     host = auth + this.host;
   } else if (this.hostname) {
     host = auth + (
-      this.hostname.indexOf(':') === -1 ?
-        this.hostname :
-        '[' + this.hostname + ']'
+      this.hostname.includes(':') ?
+        '[' + this.hostname + ']' :
+        this.hostname
     );
     if (this.port) {
       host += ':' + this.port;