Entrypoint Loaders

Because entrypoint options, like content script matches, are listed in the entrypoint's JS file, WXT has to import them during the build process to use those options when generating the manifest.

There are two options for loading your entrypoints:

1. vite-node - default as of v0.19.0
2. jiti (DEPRECATED, will be removed in v0.20.0) - Default before v0.19.0

vite-node

Since 0.19.0, WXT uses vite-node, the same tool that powers Vitest and Nuxt, to import your entrypoint files.

If you use any runtime packages that depend on webextension-polyfill, you need to add them to Vite's ssr.noExternal option:

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

Why?

This tells Vite it needs process these module's, letting WXT properly disable the polyfill in the NodeJS environment so it doesn't cause any build errors like this:

ERROR This script should only be loaded in a browser extension

To get a list of installed packages that use on webextension-polyfill, run your package manager's list command. Here's an example with PNPM:

$ pnpm why webextension-polyfill

dependencies:
@webext-core/messaging 1.4.0
└── webextension-polyfill 0.10.0
@webext-core/proxy-service 1.2.0
├─┬ @webext-core/messaging 1.4.0 peer
│ └── webextension-polyfill 0.10.0
└── webextension-polyfill 0.12.0 peer

devDependencies:
@wxt-dev/module-vue 1.0.0
└─┬ wxt 0.19.0-alpha1 peer
  └── webextension-polyfill 0.12.0
webextension-polyfill 0.12.0
wxt 0.19.0-alpha1
└── webextension-polyfill 0.12.0

Ignoring WXT itself (it's added automatically for you), there are three packages that depend on the polyfill: @wxt-dev/module-vue, @webext-core/messaging, and @webext-core/proxy-service. Since the vue module is a build dependency, with no runtime code, you don't have to add it. That means for this case, you need to add @webext-core/messaging, and @webext-core/proxy-service, as shown in the original code snippet.

jiti

The original method WXT used to import TS files. However, because it doesn't support vite plugins like vite-node, there is one main caveot to it's usage: module side-effects.

To enable jiti:

export default defineConfig({
  entrypointLoader: 'jiti',
});

You cannot use imported variables outside the main function in JS entrypoints. This includes options, as shown below:

// entrypoints/content.ts
import { GOOGLE_MATCHES } from '~/utils/match-patterns';

export default defineContentScript({
  matches: GOOGLE_MATCHES,
  main() {
    // ...
  },
});

$ wxt build
wxt build

WXT 0.14.1
ℹ Building chrome-mv3 for production with Vite 5.0.5
✖ Command failed after 360 ms

[8:55:54 AM]  ERROR  entrypoints/content.ts: Cannot use imported variable "GOOGLE_MATCHES" before main function. See https://wxt.dev/guide/entrypoints.html#side-effects

This throws an error because WXT needs to import each entrypoint during the build process to extract its definition (containing the match, runAt, include/exclude, etc.) to render the manifest.json correctly. Before loading an entrypoint, a transformation is applied to remove all imports. This prevents imported modules (local or NPM) with side-effects from running during the build process, potentially throwing an error.

Why?

When importing your entrypoint to get its definition, the file is imported in a node environment, and doesn't have access to the window, chrome, or browser globals a web extension usually has access to. If WXT doesn't remove all the imports from the file, the imported modules could try and access one of these variables, throwing an error.

WARNING

See wxt-dev/wxt#336 to track the status of this bug.

Usually, this error occurs when you try to extract options into a shared file or try to run code outside the main function. To fix the example from above, use literal values when defining an entrypoint instead of importing them:

import { GOOGLE_MATCHES } from '~/utils/match-patterns'; 

export default defineContentScript({
  matches: GOOGLE_MATCHES, 
  matches: ['*//*.google.com/*'], 
  main() {
    // ...
  },
});