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Aaron 885f8f0b76 docs: Cleanup v0.21 migration guide

2026-07-26 18:02:38 -05:00

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Upgrading WXT

Overview

To upgrade WXT to the latest major version:

Install it, skipping scripts so wxt prepare doesn't run - it will probably throw an error after a major version change (we'll run it later).
```
pnpm i wxt@latest --ignore-scripts
```
Follow the upgrade steps below to fix any breaking changes.
Run wxt prepare. It should succeed and type errors will go away afterwords.
```
pnpm wxt prepare
```
Manually test to make sure both dev mode and production builds work.

For minor or patch version updates, there are no special steps. Just update it with your package manager:

pnpm i wxt@latest

Listed below are all the breaking changes you should address when upgrading to a new version of WXT.

Currently, WXT is in pre-release. This means changes to the second digit, v0.X, are considered major and have breaking changes. Once v1 is released, only major version bumps will have breaking changes.

v0.20.0 → v0.21.0

Opt Into Opening the Browser During Dev Mode

Before v0.20, web-ext was included as a dependency of WXT so that the browser could open automatically. However, it is quite heavy and not everyone uses this feature.

So in v0.21, web-ext is now an optional peer dependency - if it's installed, the browser will be opened automatically. If not, the feature is disabled.

To continue opening the browser automatically: Install web-ext as a dependency
```
pnpm add -D web-ext
```
If you don't use this feature: Don't install it and you can delete any web-ext.config.ts options and/or remove any webExt.enabled: false config

You can still disable this behavior by setting webExt.enabled: false in your wxt.config.ts file or web-ext.config.ts file if the package is present.

Projects created with wxt init will include web-ext in their package.json, opting new projects into this feature by default.

Template Variable Changes

The {{version}} variable's value in the artifactTemplate and sourcesTemplate config has changed:

Old: manifest.version_name ?? manifest.version
New: manifest.version

If you don't customize artifactTemplate or sourcesTemplate, this does not effect you.

If you have a custom template for one of these options, replace {{version}} with {{versionName}} to maintain the same behavior as before.

For more info on the difference between manifest.version_name and manifest.version, see the Manifest Config docs.

`createShadowRoot` DOM Changes

@webext-core/isolated-element was upgraded to v3. This release changes the internal structure of the shadow root's DOM, simplifying it from a full <html> document to just a div:

:::code-group

<html>
  <head>
    <style>
      ...
    </style>
  </head>
  <body>
    ...your app
  </body>
</html>

<style>
  ...
</style>
<div>...your app</div>

:::

Historically, CSS frameworks haven't had good support for shadow roots, we used to need the full <html> structure for styles to be applied correctly. But that has change this past few years, frameworks have started to include the host: selector alongside root:, which is required for base styles to be applied to the shadow root's host element:

:root { /* [!code --] */
:root, :host { /* [!code ++] */
    /* base styles... */
}

If you use createShadowRootUi, see if your UI looks the same after this update without any changes.

If the styles are broken, you can continue using the full <html> structure by installing the v1 of @webext-core/isolated-element - WXT will respect whatever version of the package is listed in your package.json.

pnpm add @webext-core/isolated-element@^1

New Deprecations in v0.20

Deprecated APIs will be removed in the next major release.

wxt.config.runnerConfig renamed to wxt.config.webExt.

v0.19.0 → v0.20.0

v0.20 is a big release! There are lots of breaking changes because this version is intended to be a release candidate for v1.0. If all goes well, v1.0 will be released with no additional breaking changes.

:::tip Read through all the changes once before updating your code. :::

`webextension-polyfill` Removed

WXT's browser no longer uses the webextension-polyfill!

:::details Why? See https://github.com/wxt-dev/wxt/issues/784 :::

To upgrade, you have two options:

Stop using the polyfill

If you're already using extensionApi: "chrome", then you're not using the polyfill and there is nothing to change!

Otherwise there is only one change: browser.runtime.onMessage no longer supports using promises to return a response:

browser.runtime.onMessage.addListener(async () => { // [!code --]
  const res = await someAsyncWork(); // [!code --]
  return res; // [!code --]
browser.runtime.onMessage.addListener(async (_message, _sender, sendResponse) => { // [!code ++]
  someAsyncWork().then((res) => { // [!code ++]
    sendResponse(res); // [!code ++]
  }); // [!code ++]
  return true; // [!code ++]
});

Continue using the polyfill - If you want to keep using the polyfill, you can! One less thing to worry about during this upgrade.
- Install webextension-polyfill and WXT's new polyfill module:
```
pnpm i webextension-polyfill @wxt-dev/webextension-polyfill
```
- Add the WXT module to your config:
```
export default defineConfig({
  modules: ['@wxt-dev/webextension-polyfill'],
});
```

The new browser object (and types) is backed by WXT's new package: @wxt-dev/browser. This package continues WXT's mission of providing useful packages for the whole community. Just like @wxt-dev/storage, @wxt-dev/i18n, @wxt-dev/analytics, it is designed to be easy to use in any web extension project, not just those using WXT, and provides a consistent API across all browsers and manifest versions.

`extensionApi` Config Removed

The extensionApi config has been removed. Before, this config provided a way to opt into using the new browser object prior to v0.20.0.

Remove it from your wxt.config.ts file if present:

export default defineConfig({
  extensionApi: 'chrome', // [!code --]
});

Extension API Type Changes

With the new browser introduced in v0.20, how you access types has changed. WXT now provides types based on @types/chrome instead of @types/webextension-polyfill.

These types are more up-to-date with MV3 APIs, contain less bugs, are better organized, and don't have any auto-generated names.

To access types, use the new Browser namespace from wxt/browser:

import type { Runtime } from 'wxt/browser'; // [!code --]
import type { Browser } from 'wxt/browser'; // [!code ++]

function getMessageSenderUrl(sender: Runtime.MessageSender): string { // [!code --]
function getMessageSenderUrl(sender: Browser.runtime.MessageSender): string { // [!code ++]
  // ...
}

If you use auto-imports, Browser will be available without manually importing it.

Not all type names will be the same as what @types/webextension-polyfill provides. You'll have to find the new type names by looking at the types of the browser.* API's you use.

`public/` and `modules/` Directories Moved

The default location for the public/ and modules/ directories have changed to better align with standards set by other frameworks (Nuxt, Next, Astro, etc). Now, each path is relative to the project's root directory, not the src directory.

If you follow the default folder structure, you don't need to make any changes.

If you set a custom srcDir, you have two options:

Move the your public/ and modules/ directories to the project root:

 📂 {rootDir}/
    📁 modules/ <!-- [!code ++] -->
    📁 public/ <!-- [!code ++] -->
    📂 src/
       📁 components/
       📁 entrypoints/
       📁 modules/ <!-- [!code --] -->
       📁 public/ <!-- [!code --] -->
       📁 utils/
       📄 app.config.ts
    📄 wxt.config.ts

Keep the folders in the same place and update your project config:

export default defineConfig({
  srcDir: 'src',
  publicDir: 'src/public', // [!code ++]
  modulesDir: 'src/modules', // [!code ++]
});

Import Path Changes and `#imports`

The APIs exported by wxt/sandbox, wxt/client, or wxt/storage have moved to individual exports under the wxt/utils/* path.

:::details Why? As WXT grows and more utilities are added, any helper with side-effects will not be tree-shaken out of your final bundle.

This can cause problems because not every API used by these side-effects is available in every type of entrypoint. Some APIs can only be used in the background, sandboxed pages can't use any extension API, etc. This was leading to JS throwing errors in the top-level scope, preventing your code from running.

Splitting each util into it's own module solves this problem, making sure you're only importing APIs and side-effects into entrypoints they can run in. :::

Refer to the updated API Reference to see the list of new import paths.

However, you don't need to memorize or learn the new import paths! v0.20 introduces a new virtual module, #imports, that abstracts all this away from developers. See the blog post for more details about how this module works.

So to upgrade, just replace any imports from wxt/storage, wxt/client, and wxt/sandbox with an import to the new #imports module:

import { storage } from 'wxt/storage'; // [!code --]
import { defineContentScript } from 'wxt/sandbox'; // [!code --]
import { ContentScriptContext, useAppConfig } from 'wxt/client'; // [!code --]
import { storage } from '#imports'; // [!code ++]
import { defineContentScript } from '#imports'; // [!code ++]
import { ContentScriptContext, getAppConfig } from '#imports'; // [!code ++]

You can combine the imports into a single import statement, but it's easier to just find/replace each statement.

import { storage } from 'wxt/storage'; // [!code --]
import { defineContentScript } from 'wxt/sandbox'; // [!code --]
import { ContentScriptContext, useAppConfig } from 'wxt/client'; // [!code --]
import {
  // [!code ++]
  storage, // [!code ++]
  defineContentScript, // [!code ++]
  ContentScriptContext, // [!code ++]
  getAppConfig, // [!code ++]
} from '#imports'; // [!code ++]

:::tip Before types will work, you'll need to run wxt prepare after installing v0.20 to generate the new TypeScript declarations. :::

`createShadowRootUi` CSS Changes

WXT now resets styles inherited from the webpage (visibility, color, font-size, etc.) by setting all: initial inside the shadow root.

:::warning This doesn't effect rem units. You should continue using postcss-rem-to-px or an equivalent library if the webpage sets the HTML element's font-size. :::

If you use createShadowRootUi:

Remove any manual CSS overrides that reset the style of specific websites. For example:

body { /* [!code --] */
  /* Override Reddit's default "hidden" visibility on elements */ /* [!code --] */
  visibility: visible !important; /* [!code --] */
} /* [!code --] */

Double check that your UI looks the same as before.

If you run into problems with the new behavior, you can disable it and continue using your current CSS:

const ui = await createShadowRootUi({
  inheritStyles: true, // [!code ++]
  // ...
});

Default Output Directories Changed

The default value for the outDirTemplate config has changed. Now, different build modes are output to different directories:

--mode production → .output/chrome-mv3: Production builds are unchanged
--mode development → .output/chrome-mv3-dev: Dev mode now has a -dev suffix so it doesn't overwrite production builds
--mode custom → .output/chrome-mv3-custom: Other custom modes end with a -[mode] suffix

To use the old behavior, writing all output to the same directory, set the outDirTemplate option:

export default defineConfig({
  outDirTemplate: '{{browser}}-mv{{manifestVersion}}', // [!code ++]
});

:::warning If you've previously loaded the extension into your browser manually for development, you'll need to uninstall and re-install it from the new dev output directory. :::

Deprecated APIs Removed

entrypointLoader option: WXT now uses vite-node for importing entrypoints during the build process.

This was deprecated in v0.19.0, see the v0.19 section for migration steps.

transformManifest option: Use the build:manifestGenerated hook to transform the manifest instead:

export default defineConfig({
  transformManifest(manifest) { // [!code --]
  hooks: { // [!code ++]
    'build:manifestGenerated': (_, manifest) => { // [!code ++]
       // ...
    }, // [!code ++]
  },
});

New Deprecations

`runner` APIs Renamed

To improve consistency with the web-ext.config.ts filename, the "runner" API and config options have been renamed. You can continue using the old names, but they have been deprecated and will be removed in a future version:

The runner option has been renamed to webExt:

export default defineConfig({
  runner: { // [!code --]
  webExt: { // [!code ++]
    startUrls: ["https://wxt.dev"],
  },
});

defineRunnerConfig has been renamed to defineWebExtConfig:

import { defineRunnerConfig } from 'wxt'; // [!code --]
import { defineWebExtConfig } from 'wxt'; // [!code ++]

The ExtensionRunnerConfig type has been renamed to WebExtConfig

import type { ExtensionRunnerConfig } from 'wxt'; // [!code --]
import type { WebExtConfig } from 'wxt'; // [!code ++]

v0.18.5 → v0.19.0

`vite-node` Entrypoint Loader

The default entrypoint loader has changed to vite-node. If you use any NPM packages that depend on the webextension-polyfill, you need to add them to Vite's ssr.noExternal option:

export default defineConfig({
  vite: () => ({ // [!code ++]
    ssr: { // [!code ++]
      noExternal: ['@webext-core/messaging', '@webext-core/proxy-service'], // [!code ++]
    }, // [!code ++]
  }), // [!code ++]
});

Read the full docs for more information.

:::details This change enables:

Importing variables and using them in the entrypoint options:

import { GOOGLE_MATCHES } from '~/utils/constants'

export default defineContentScript({
  matches: [GOOGLE_MATCHES],
  main: () => ...,
})

Using Vite-specific APIs like import.meta.glob to define entrypoint options:

const providers: Record<string, any> = import.meta.glob('../providers/*', {
  eager: true,
});

export default defineContentScript({
  matches: Object.values(providers).flatMap(
    (provider) => provider.default.paths,
  ),
  async main() {
    console.log('Hello content.');
  },
});

Basically, you can now import and do things outside the main function of the entrypoint - you could not do that before. Still though, be careful. It is recommended to avoid running code outside the main function to keep your builds fast.

:::

To continue using the old approach, add the following to your wxt.config.ts file:

export default defineConfig({
  entrypointLoader: 'jiti', // [!code ++]
});

:::warning entrypointLoader: "jiti" is deprecated and will be removed in the next major version. :::

Drop CJS Support

WXT no longer ships with Common JS support. If you're using CJS, here's your migration steps:

Add "type": "module" to your package.json.
Change the file extension of any .js files that use CJS syntax to .cjs, or update them to use EMS syntax.

Vite also provides steps for migrating to ESM. Check them out for more details: https://vitejs.dev/guide/migration#deprecate-cjs-node-api

v0.18.0 → v0.18.5

When this version was released, it was not considered a breaking change... but it should have been.

New `modules/` Directory

WXT now recognizes the modules/ directory as a folder containing WXT modules.

If you already have <srcDir>/modules or <srcDir>/Modules directory, wxt prepare and other commands will fail.

You have two options:

[Recommended] Keep your files where they are and tell WXT to look in a different folder:

export default defineConfig({
  modulesDir: 'wxt-modules', // defaults to "modules"
});

Rename your modules directory to something else.

v0.17.0 → v0.18.0

Automatic MV3 `host_permissions` to MV2 `permissions`

Out of an abundance of caution, this change has been marked as a breaking change because permission generation is different.

If you list host_permissions in your wxt.config.ts's manifest and have released your extension, double check that your permissions and host_permissions have not changed for all browsers you target in your .output/*/manifest.json files. Permission changes can cause the extension to be disabled on update, and can cause a drop in users, so be sure to double check for differences compared to the previous manifest version.

v0.16.0 → v0.17.0

Storage - `defineItem` Requires `defaultValue` Option

If you were using defineItem with versioning and no default value, you will need to add defaultValue: null to the options and update the first type parameter:

const item = storage.defineItem<number>("local:count", { // [!code --]
const item = storage.defineItem<number | null>("local:count", { // [!code ++]
defaultValue: null, // [!code ++]
  version: ...,
  migrations: ...,
})

The defaultValue property is now required if passing in the second options argument.

If you exclude the second options argument, it will default to being nullable, as before.

const item: WxtStorageItem<number | null> =
  storage.defineItem<number>('local:count');
const value: number | null = await item.getValue();

Storage - Fix Types In `watch` Callback

If you don't use TypeScript, this isn't a breaking change, this is just a type change.

const item = storage.defineItem<number>('local:count', { defaultValue: 0 });
item.watch((newValue: number | null, oldValue: number | null) => { // [!code --]
item.watch((newValue: number, oldValue: number) => { // [!code ++]
  // ...
});

v0.15.0 → v0.16.0

Output Directory Structure Changed

JS entrypoints in the output directory have been moved. Unless you're doing some kind of post-build work referencing files, you don't have to make any changes.

.output/
  <target>/
    chunks/
      some-shared-chunk-<hash>.js
      popup-<hash>.js // [!code --]
    popup.html
    popup.html
    popup.js // [!code ++]

v0.14.0 → v0.15.0

Renamed `zip.ignoredSources` to `zip.excludeSources`

export default defineConfig({
  zip: {
    ignoredSources: [
      /*...*/
    ], // [!code --]
    excludeSources: [
      /*...*/
    ], // [!code ++]
  },
});

Renamed Undocumented Constants

Renamed undocumented constants for detecting the build config at runtime in #380. Now documented here: https://wxt.dev/guide/essentials/config/environment-variables.html#built-in-environment-variables

__BROWSER__ → import.meta.env.BROWSER
__COMMAND__ → import.meta.env.COMMAND
__MANIFEST_VERSION__ → import.meta.env.MANIFEST_VERSION
__IS_CHROME__ → import.meta.env.CHROME
__IS_FIREFOX__ → import.meta.env.FIREFOX
__IS_SAFARI__ → import.meta.env.SAFARI
__IS_EDGE__ → import.meta.env.EDGE
__IS_OPERA__ → import.meta.env.OPERA

v0.13.0 → v0.14.0

Content Script UI API changes

createContentScriptUi and createContentScriptIframe, and some of their options, have been renamed:

createContentScriptUi({ ... }) → createShadowRootUi({ ... })
createContentScriptIframe({ ... }) → createIframeUi({ ... })
type: "inline" | "overlay" | "modal" has been changed to position: "inline" | "overlay" | "modal"
onRemove is now called before the UI is removed from the DOM, previously it was called after the UI was removed
mount option has been renamed to onMount, to better match the related option, onRemove.

v0.12.0 → v0.13.0

New `wxt/storage` APIs

wxt/storage no longer relies on unstorage. Some unstorage APIs, like prefixStorage, have been removed, while others, like snapshot, are methods on the new storage object. Most of the standard usage remains the same. See https://wxt.dev/guide/storage and https://wxt.dev/api/reference/wxt/storage/ for more details (#300)

v0.11.0 → v0.12.0

API Exports Changed

defineContentScript and defineBackground are now exported from wxt/sandbox instead of wxt/client. (#284)

If you use auto-imports, no changes are required.

If you have disabled auto-imports, you'll need to manually update your import statements:

import { defineBackground, defineContentScript } from 'wxt/client'; // [!code --]
import { defineBackground, defineContentScript } from 'wxt/sandbox'; // [!code ++]

v0.10.0 → v0.11.0

Vite 5

You will need to update any other Vite plugins to a version that supports Vite 5.

v0.9.0 → v0.10.0

Extension Icon Discovery

WXT no longer discovers icons other than .png files. If you previously used .jpg, .jpeg, .bmp, or .svg, you'll need to convert your icons to .png files or manually add them to the manifest inside your wxt.config.ts file.

v0.8.0 → v0.9.0

Removed `WebWorker` Types by Default

Removed "WebWorker" types from .wxt/tsconfig.json. These types are useful for MV3 projects using a service worker.

To add them back to your project, add the following to your project's TSConfig:

{
  "extends": "./.wxt/tsconfig.json",
  "compilerOptions": {
    // [!code ++]
    "lib": ["ESNext", "DOM", "WebWorker"] // [!code ++]
  } // [!code ++]
}

v0.7.0 → v0.8.0

`defineUnlistedScript`

Unlisted scripts must now export default defineUnlistedScript(...).

`BackgroundDefinition` Type

Rename BackgroundScriptDefintition to BackgroundDefinition.

v0.6.0 → v0.7.0

Content Script CSS Output Location Changed

Content script CSS used to be output to assets/<name>.css, but is now content-scripts/<name>.css to match the docs.

v0.5.0 → v0.6.0

Require a Function for `vite` Config

The vite config option must now be a function. If you were using an object before, change it from vite: { ... } to vite: () => ({ ... }).

v0.4.0 → v0.5.0

Revert Move Public Directory

Change default publicDir to from <rootDir>/public to <srcDir>/public.

v0.3.0 → v0.4.0

Update Default Path Aliases

Use relative path aliases inside .wxt/tsconfig.json.

v0.2.0 → v0.3.0

Move Public Directory

Change default publicDir to from <srcDir>/public to <rootDir>/public.

Improve Type Safety

Add type safety to browser.runtime.getURL.

v0.1.0 → v0.2.0

Rename `defineBackground`

Rename defineBackgroundScript to defineBackground.

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