diff --git a/examples/cms-agilitycms/lib/preview.ts b/examples/cms-agilitycms/lib/preview.ts
index 42e456df04b67..dc0b0a7dd7c6f 100644
--- a/examples/cms-agilitycms/lib/preview.ts
+++ b/examples/cms-agilitycms/lib/preview.ts
@@ -88,7 +88,7 @@ export async function validatePreview({ agilityPreviewKey, slug, contentID }) {
   }
 
   //sanitize incoming key (replace spaces with '+')
-  if (agilityPreviewKey.indexOf(` `) > -1) {
+  if (agilityPreviewKey.includes(` `)) {
     agilityPreviewKey = agilityPreviewKey.split(` `).join(`+`)
   }
 
diff --git a/packages/next-codemod/bin/cli.ts b/packages/next-codemod/bin/cli.ts
index 5abf870f8090e..d388df289f0dc 100644
--- a/packages/next-codemod/bin/cli.ts
+++ b/packages/next-codemod/bin/cli.ts
@@ -27,7 +27,7 @@ export function checkGitStatus(force) {
     clean = isGitClean.sync(process.cwd())
     errorMessage = 'Git directory is not clean'
   } catch (err) {
-    if (err && err.stderr && err.stderr.indexOf('Not a git repository') >= 0) {
+    if (err && err.stderr && err.stderr.includes('Not a git repository')) {
       clean = true
     }
   }
diff --git a/packages/next-swc/crates/next-core/js/src/overlay/internal/components/Overlay/maintain--tab-focus.ts b/packages/next-swc/crates/next-core/js/src/overlay/internal/components/Overlay/maintain--tab-focus.ts
index 17db3344c5b54..0771c0fe6eae6 100644
--- a/packages/next-swc/crates/next-core/js/src/overlay/internal/components/Overlay/maintain--tab-focus.ts
+++ b/packages/next-swc/crates/next-core/js/src/overlay/internal/components/Overlay/maintain--tab-focus.ts
@@ -1136,7 +1136,7 @@ function isUserModifyWritable(style) {
   // https://www.w3.org/TR/1999/WD-css3-userint-19990916#user-modify
   // https://github.com/medialize/ally.js/issues/17
   var userModify = style.webkitUserModify || ''
-  return Boolean(userModify && userModify.indexOf('write') !== -1)
+  return Boolean(userModify && userModify.includes('write'))
 }
 
 function hasCssOverflowScroll(style) {
diff --git a/packages/next/src/client/components/react-dev-overlay/hot-reloader-client.tsx b/packages/next/src/client/components/react-dev-overlay/hot-reloader-client.tsx
index e02cf016d6aa9..679796e239624 100644
--- a/packages/next/src/client/components/react-dev-overlay/hot-reloader-client.tsx
+++ b/packages/next/src/client/components/react-dev-overlay/hot-reloader-client.tsx
@@ -469,9 +469,9 @@ export default function HotReload({
   useEffect(() => {
     const handler = (event: MessageEvent<PongEvent>) => {
       if (
-        event.data.indexOf('action') === -1 &&
+        !event.data.includes('action') &&
         // TODO-APP: clean this up for consistency
-        event.data.indexOf('pong') === -1
+        !event.data.includes('pong')
       ) {
         return
       }
diff --git a/packages/next/src/client/dev/error-overlay/format-webpack-messages.ts b/packages/next/src/client/dev/error-overlay/format-webpack-messages.ts
index 82a025f32f794..618bfb2af4d08 100644
--- a/packages/next/src/client/dev/error-overlay/format-webpack-messages.ts
+++ b/packages/next/src/client/dev/error-overlay/format-webpack-messages.ts
@@ -31,7 +31,7 @@ const WEBPACK_BREAKING_CHANGE_POLYFILLS =
   '\n\nBREAKING CHANGE: webpack < 5 used to include polyfills for node.js core modules by default.'
 
 function isLikelyASyntaxError(message: string) {
-  return stripAnsi(message).indexOf(friendlySyntaxErrorLabel) !== -1
+  return stripAnsi(message).includes(friendlySyntaxErrorLabel)
 }
 
 let hadMissingSassError = false
diff --git a/packages/next/src/client/dev/error-overlay/hot-dev-client.ts b/packages/next/src/client/dev/error-overlay/hot-dev-client.ts
index 8bbd9840989a1..c1f1522142b43 100644
--- a/packages/next/src/client/dev/error-overlay/hot-dev-client.ts
+++ b/packages/next/src/client/dev/error-overlay/hot-dev-client.ts
@@ -64,7 +64,7 @@ export default function connect() {
   register()
 
   addMessageListener((event) => {
-    if (event.data.indexOf('action') === -1) return
+    if (!event.data.includes('action')) return
 
     try {
       processMessage(event)
diff --git a/packages/next/src/client/dev/on-demand-entries-client.ts b/packages/next/src/client/dev/on-demand-entries-client.ts
index 94cfc4133f80a..a1b9c9ca7bc8b 100644
--- a/packages/next/src/client/dev/on-demand-entries-client.ts
+++ b/packages/next/src/client/dev/on-demand-entries-client.ts
@@ -27,7 +27,7 @@ export default async (page?: string) => {
   }
 
   addMessageListener((event) => {
-    if (event.data.indexOf('{') === -1) return
+    if (!event.data.includes('{')) return
     try {
       const payload = JSON.parse(event.data)
       // don't attempt fetching the page if we're already showing
diff --git a/packages/next/src/client/next-dev.ts b/packages/next/src/client/next-dev.ts
index 28a35e08c0c6c..12e7a7fe92a47 100644
--- a/packages/next/src/client/next-dev.ts
+++ b/packages/next/src/client/next-dev.ts
@@ -55,7 +55,7 @@ initialize({ webpackHMR })
       let buildIndicatorHandler: any = () => {}
 
       function devPagesManifestListener(event: any) {
-        if (event.data.indexOf('devPagesManifest') !== -1) {
+        if (event.data.includes('devPagesManifest')) {
           fetch(
             `${assetPrefix}/_next/static/development/_devPagesManifest.json`
           )
@@ -66,9 +66,9 @@ initialize({ webpackHMR })
             .catch((err) => {
               console.log(`Failed to fetch devPagesManifest`, err)
             })
-        } else if (event.data.indexOf('middlewareChanges') !== -1) {
+        } else if (event.data.includes('middlewareChanges')) {
           return window.location.reload()
-        } else if (event.data.indexOf('serverOnlyChanges') !== -1) {
+        } else if (event.data.includes('serverOnlyChanges')) {
           const { pages } = JSON.parse(event.data)
 
           // Make sure to reload when the dev-overlay is showing for an
diff --git a/packages/next/src/shared/lib/loadable.tsx b/packages/next/src/shared/lib/loadable.tsx
index fabed3fd27ce9..1592d98551093 100644
--- a/packages/next/src/shared/lib/loadable.tsx
+++ b/packages/next/src/shared/lib/loadable.tsx
@@ -101,7 +101,7 @@ function createLoadableComponent(loadFn: any, options: any) {
     if (moduleIds) {
       READY_INITIALIZERS.push((ids: any) => {
         for (const moduleId of moduleIds) {
-          if (ids.indexOf(moduleId) !== -1) {
+          if (ids.includes(moduleId)) {
             return init()
           }
         }
diff --git a/packages/next/src/shared/lib/router/utils/format-url.ts b/packages/next/src/shared/lib/router/utils/format-url.ts
index efc9df8c4ea47..990dbde7bf7b5 100644
--- a/packages/next/src/shared/lib/router/utils/format-url.ts
+++ b/packages/next/src/shared/lib/router/utils/format-url.ts
@@ -91,7 +91,7 @@ export function formatWithValidation(url: UrlObject): string {
   if (process.env.NODE_ENV === 'development') {
     if (url !== null && typeof url === 'object') {
       Object.keys(url).forEach((key) => {
-        if (urlObjectKeys.indexOf(key) === -1) {
+        if (!urlObjectKeys.includes(key)) {
           console.warn(
             `Unknown key passed via urlObject into url.format: ${key}`
           )
diff --git a/packages/react-dev-overlay/src/internal/helpers/launchEditor.ts b/packages/react-dev-overlay/src/internal/helpers/launchEditor.ts
index 593926e11b1d1..9d4dd4efd1685 100644
--- a/packages/react-dev-overlay/src/internal/helpers/launchEditor.ts
+++ b/packages/react-dev-overlay/src/internal/helpers/launchEditor.ts
@@ -226,7 +226,7 @@ function guessEditor(): string[] {
       const processNames = Object.keys(COMMON_EDITORS_MACOS)
       for (let i = 0; i < processNames.length; i++) {
         const processName = processNames[i]
-        if (output.indexOf(processName) !== -1) {
+        if (output.includes(processName)) {
           return [(COMMON_EDITORS_MACOS as any)[processName]]
         }
       }
@@ -242,7 +242,7 @@ function guessEditor(): string[] {
       for (let i = 0; i < runningProcesses.length; i++) {
         const processPath = runningProcesses[i].trim()
         const processName = path.basename(processPath)
-        if (COMMON_EDITORS_WIN.indexOf(processName) !== -1) {
+        if (COMMON_EDITORS_WIN.includes(processName)) {
           return [processPath]
         }
       }
@@ -256,7 +256,7 @@ function guessEditor(): string[] {
       const processNames = Object.keys(COMMON_EDITORS_LINUX)
       for (let i = 0; i < processNames.length; i++) {
         const processName = processNames[i]
-        if (output.indexOf(processName) !== -1) {
+        if (output.includes(processName)) {
           return [(COMMON_EDITORS_LINUX as any)[processName] as string]
         }
       }
diff --git a/test/lib/next-webdriver.ts b/test/lib/next-webdriver.ts
index c48b4a6a0f38c..34aab288d5804 100644
--- a/test/lib/next-webdriver.ts
+++ b/test/lib/next-webdriver.ts
@@ -120,7 +120,7 @@ export default async function webdriver(
 
         // if it's not a Next.js app return
         if (
-          document.documentElement.innerHTML.indexOf('__NEXT_DATA__') === -1 &&
+          !document.documentElement.innerHTML.includes('__NEXT_DATA__') &&
           // @ts-ignore next exists on window if it's a Next.js page.
           typeof ((window as any).next && (window as any).next.version) ===
             'undefined'