rsnext/errors/no-unwanted-polyfillio.mdx

---
title: No Unwanted Polyfill.io
---

> Prevent duplicate polyfills from Polyfill.io.

## Why This Error Occurred

You are using polyfills from Polyfill.io and including polyfills already shipped with Next.js. This unnecessarily increases page weight which can affect loading performance.

## Possible Ways to Fix It

Remove all duplicate polyfills. If you need to add polyfills but are not sure if Next.js already includes it, take a look at the list of [supported browsers and features](/docs/architecture/supported-browsers).

## Useful Links

- [Supported Browsers and Features](/docs/architecture/supported-browsers)
docs: Migrate error messages to MDX and App Router. (#52038) This PR is part of a larger effort to migrate error messages to MDX and use App Router: https://github.com/vercel/front/pull/23459 2023-07-05 15:11:16 +02:00			`---`
			`title: No Unwanted Polyfill.io`
			`---`
Adds consistency to ESLint rules. (#34335) * Adds consistency to ESLint rules. * Fixes lint errors. * Fixes manifest. * Adds missing title. * Fixes copy / paste error. Co-authored-by: Lee Robinson <me@leerob.io> * Update errors/no-script-in-document.md Co-authored-by: Lee Robinson <me@leerob.io> * Update errors/no-sync-scripts.md Co-authored-by: Lee Robinson <me@leerob.io> * Updates a couple of rule descriptions. * Adds redirects. * Fixes unit tests. * Removes duplicated section. * Updates `no-before-interactive-script-outside-document` description. * Fixes lint. * Fixes integration tests. * Adds description to `no-before-interactive-script-outside-document` documentation. * Removes `link-passhref` from rules list. * Updates remaining `pages/_middleware.js` references. * Adds consistancy to messaging in new `no-styled-jsx-in-document` rule. * Apply suggestions from code review * Apply suggestions from code review Co-authored-by: Lee Robinson <me@leerob.io> Co-authored-by: Tim Neutkens <tim@timneutkens.nl> Co-authored-by: JJ Kasper <jj@jjsweb.site> 2022-06-14 04:17:42 +02:00
			`> Prevent duplicate polyfills from Polyfill.io.`
Adds ESLint with default rule-set (#23702) This PR re-includes ESLint with some notable changes, namely a guided setup similar to how TypeScript is instantiated in a Next.js application. To add ESLint to a project, developers will have to create an `.eslintrc` file in the root of their project or add an empty `eslintConfig` object to their `package.json` file. ```js touch .eslintrc ``` Then running `next build` will show instructions to install the required packages needed: <img width="862" alt="Screen Shot 2021-04-19 at 7 38 27 PM" src="https://user-images.githubusercontent.com/12476932/115316182-dfd51b00-a146-11eb-830c-90bad20ed151.png"> Once installed and `next build` is run again, `.eslintrc` will be automatically configured to include the default config: ```json { "extends": "next" } ``` In addition to this change: - The feature is now under the experimental flag and requires opt-in. After testing and feedback, it will be switched to the top-level namespace and turned on by default. - A new ESLint shareable configuration package is included that can be extended in any application with `{ extends: 'next' }` - This default config extends recommended rule sets from [`eslint-plugin-react`](https://www.npmjs.com/package/eslint-plugin-react), [`eslint-plugin-react-hooks`](https://www.npmjs.com/package/eslint-plugin-react-hooks), and [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next) - All rules in [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next) have been modified to include actionable links that show more information to help resolve each issue 2021-04-30 13:09:07 +02:00
docs: Migrate error messages to MDX and App Router. (#52038) This PR is part of a larger effort to migrate error messages to MDX and use App Router: https://github.com/vercel/front/pull/23459 2023-07-05 15:11:16 +02:00			`## Why This Error Occurred`
Adds ESLint with default rule-set (#23702) This PR re-includes ESLint with some notable changes, namely a guided setup similar to how TypeScript is instantiated in a Next.js application. To add ESLint to a project, developers will have to create an `.eslintrc` file in the root of their project or add an empty `eslintConfig` object to their `package.json` file. ```js touch .eslintrc ``` Then running `next build` will show instructions to install the required packages needed: <img width="862" alt="Screen Shot 2021-04-19 at 7 38 27 PM" src="https://user-images.githubusercontent.com/12476932/115316182-dfd51b00-a146-11eb-830c-90bad20ed151.png"> Once installed and `next build` is run again, `.eslintrc` will be automatically configured to include the default config: ```json { "extends": "next" } ``` In addition to this change: - The feature is now under the experimental flag and requires opt-in. After testing and feedback, it will be switched to the top-level namespace and turned on by default. - A new ESLint shareable configuration package is included that can be extended in any application with `{ extends: 'next' }` - This default config extends recommended rule sets from [`eslint-plugin-react`](https://www.npmjs.com/package/eslint-plugin-react), [`eslint-plugin-react-hooks`](https://www.npmjs.com/package/eslint-plugin-react-hooks), and [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next) - All rules in [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next) have been modified to include actionable links that show more information to help resolve each issue 2021-04-30 13:09:07 +02:00
Adds consistency to ESLint rules. (#34335) * Adds consistency to ESLint rules. * Fixes lint errors. * Fixes manifest. * Adds missing title. * Fixes copy / paste error. Co-authored-by: Lee Robinson <me@leerob.io> * Update errors/no-script-in-document.md Co-authored-by: Lee Robinson <me@leerob.io> * Update errors/no-sync-scripts.md Co-authored-by: Lee Robinson <me@leerob.io> * Updates a couple of rule descriptions. * Adds redirects. * Fixes unit tests. * Removes duplicated section. * Updates `no-before-interactive-script-outside-document` description. * Fixes lint. * Fixes integration tests. * Adds description to `no-before-interactive-script-outside-document` documentation. * Removes `link-passhref` from rules list. * Updates remaining `pages/_middleware.js` references. * Adds consistancy to messaging in new `no-styled-jsx-in-document` rule. * Apply suggestions from code review * Apply suggestions from code review Co-authored-by: Lee Robinson <me@leerob.io> Co-authored-by: Tim Neutkens <tim@timneutkens.nl> Co-authored-by: JJ Kasper <jj@jjsweb.site> 2022-06-14 04:17:42 +02:00			`You are using polyfills from Polyfill.io and including polyfills already shipped with Next.js. This unnecessarily increases page weight which can affect loading performance.`
Adds ESLint with default rule-set (#23702) This PR re-includes ESLint with some notable changes, namely a guided setup similar to how TypeScript is instantiated in a Next.js application. To add ESLint to a project, developers will have to create an `.eslintrc` file in the root of their project or add an empty `eslintConfig` object to their `package.json` file. ```js touch .eslintrc ``` Then running `next build` will show instructions to install the required packages needed: <img width="862" alt="Screen Shot 2021-04-19 at 7 38 27 PM" src="https://user-images.githubusercontent.com/12476932/115316182-dfd51b00-a146-11eb-830c-90bad20ed151.png"> Once installed and `next build` is run again, `.eslintrc` will be automatically configured to include the default config: ```json { "extends": "next" } ``` In addition to this change: - The feature is now under the experimental flag and requires opt-in. After testing and feedback, it will be switched to the top-level namespace and turned on by default. - A new ESLint shareable configuration package is included that can be extended in any application with `{ extends: 'next' }` - This default config extends recommended rule sets from [`eslint-plugin-react`](https://www.npmjs.com/package/eslint-plugin-react), [`eslint-plugin-react-hooks`](https://www.npmjs.com/package/eslint-plugin-react-hooks), and [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next) - All rules in [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next) have been modified to include actionable links that show more information to help resolve each issue 2021-04-30 13:09:07 +02:00
docs: Migrate error messages to MDX and App Router. (#52038) This PR is part of a larger effort to migrate error messages to MDX and use App Router: https://github.com/vercel/front/pull/23459 2023-07-05 15:11:16 +02:00			`## Possible Ways to Fix It`
Adds ESLint with default rule-set (#23702) This PR re-includes ESLint with some notable changes, namely a guided setup similar to how TypeScript is instantiated in a Next.js application. To add ESLint to a project, developers will have to create an `.eslintrc` file in the root of their project or add an empty `eslintConfig` object to their `package.json` file. ```js touch .eslintrc ``` Then running `next build` will show instructions to install the required packages needed: <img width="862" alt="Screen Shot 2021-04-19 at 7 38 27 PM" src="https://user-images.githubusercontent.com/12476932/115316182-dfd51b00-a146-11eb-830c-90bad20ed151.png"> Once installed and `next build` is run again, `.eslintrc` will be automatically configured to include the default config: ```json { "extends": "next" } ``` In addition to this change: - The feature is now under the experimental flag and requires opt-in. After testing and feedback, it will be switched to the top-level namespace and turned on by default. - A new ESLint shareable configuration package is included that can be extended in any application with `{ extends: 'next' }` - This default config extends recommended rule sets from [`eslint-plugin-react`](https://www.npmjs.com/package/eslint-plugin-react), [`eslint-plugin-react-hooks`](https://www.npmjs.com/package/eslint-plugin-react-hooks), and [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next) - All rules in [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next) have been modified to include actionable links that show more information to help resolve each issue 2021-04-30 13:09:07 +02:00
docs: Migrate error messages to MDX and App Router. (#52038) This PR is part of a larger effort to migrate error messages to MDX and use App Router: https://github.com/vercel/front/pull/23459 2023-07-05 15:11:16 +02:00			`Remove all duplicate polyfills. If you need to add polyfills but are not sure if Next.js already includes it, take a look at the list of [supported browsers and features](/docs/architecture/supported-browsers).`
Adds ESLint with default rule-set (#23702) This PR re-includes ESLint with some notable changes, namely a guided setup similar to how TypeScript is instantiated in a Next.js application. To add ESLint to a project, developers will have to create an `.eslintrc` file in the root of their project or add an empty `eslintConfig` object to their `package.json` file. ```js touch .eslintrc ``` Then running `next build` will show instructions to install the required packages needed: <img width="862" alt="Screen Shot 2021-04-19 at 7 38 27 PM" src="https://user-images.githubusercontent.com/12476932/115316182-dfd51b00-a146-11eb-830c-90bad20ed151.png"> Once installed and `next build` is run again, `.eslintrc` will be automatically configured to include the default config: ```json { "extends": "next" } ``` In addition to this change: - The feature is now under the experimental flag and requires opt-in. After testing and feedback, it will be switched to the top-level namespace and turned on by default. - A new ESLint shareable configuration package is included that can be extended in any application with `{ extends: 'next' }` - This default config extends recommended rule sets from [`eslint-plugin-react`](https://www.npmjs.com/package/eslint-plugin-react), [`eslint-plugin-react-hooks`](https://www.npmjs.com/package/eslint-plugin-react-hooks), and [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next) - All rules in [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next) have been modified to include actionable links that show more information to help resolve each issue 2021-04-30 13:09:07 +02:00
docs: Migrate error messages to MDX and App Router. (#52038) This PR is part of a larger effort to migrate error messages to MDX and use App Router: https://github.com/vercel/front/pull/23459 2023-07-05 15:11:16 +02:00			`## Useful Links`
Adds ESLint with default rule-set (#23702) This PR re-includes ESLint with some notable changes, namely a guided setup similar to how TypeScript is instantiated in a Next.js application. To add ESLint to a project, developers will have to create an `.eslintrc` file in the root of their project or add an empty `eslintConfig` object to their `package.json` file. ```js touch .eslintrc ``` Then running `next build` will show instructions to install the required packages needed: <img width="862" alt="Screen Shot 2021-04-19 at 7 38 27 PM" src="https://user-images.githubusercontent.com/12476932/115316182-dfd51b00-a146-11eb-830c-90bad20ed151.png"> Once installed and `next build` is run again, `.eslintrc` will be automatically configured to include the default config: ```json { "extends": "next" } ``` In addition to this change: - The feature is now under the experimental flag and requires opt-in. After testing and feedback, it will be switched to the top-level namespace and turned on by default. - A new ESLint shareable configuration package is included that can be extended in any application with `{ extends: 'next' }` - This default config extends recommended rule sets from [`eslint-plugin-react`](https://www.npmjs.com/package/eslint-plugin-react), [`eslint-plugin-react-hooks`](https://www.npmjs.com/package/eslint-plugin-react-hooks), and [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next) - All rules in [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next) have been modified to include actionable links that show more information to help resolve each issue 2021-04-30 13:09:07 +02:00
docs: Migrate error messages to MDX and App Router. (#52038) This PR is part of a larger effort to migrate error messages to MDX and use App Router: https://github.com/vercel/front/pull/23459 2023-07-05 15:11:16 +02:00			`- [Supported Browsers and Features](/docs/architecture/supported-browsers)`