Entrypoint Loaders

To generate the manifest and other files at build-time, WXT must import each entrypoint to get their options, like content script matches. For HTML files, this is easy. For JS/TS entrypoints, the process is more complicated.

When loading your JS/TS entrypoints, they are imported into a NodeJS environment, not the browser environment that they normally run in. This can lead to issues commonly seen when running browser-only code in a NodeJS environment, like missing global variables.

WXT does several pre-processing steps to try and prevent errors during this process:

1. Use linkedom to make a small set of browser globals (window, document, etc) available.
2. Use @webext-core/fake-browser to create a fake version of the chrome and browser globals expected by extensions.
3. Pre-process the JS/TS code, stripping out the main function then tree-shaking unused code from the file

However, this process is not perfect. It doesn't setup all the globals found in the browser and the APIs may behave differently. As such, you should avoid using browser or extension APIs outside the main function of your entrypoints!

TIP

If you're running into errors while importing entrypoints, run wxt prepare --debug to see more details about this process. When debugging, WXT will print out the pre-processed code to help you identify issues.

Once the environment has been polyfilled and your code pre-processed, it's up the entrypoint loader to import your code, extracting the options from the default export.

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. It re-uses the same vite config used when building your extension, making it the most stable entrypoint loader.

jiti

To enable jiti:

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

This is the original method WXT used to import TS files. However, because it doesn't support vite plugins like vite-node, it does one additional pre-processing step: It removes ALL imports from your code.

That means you cannot use imported variables outside the main function in JS entrypoints, like for content script matches or other options:

// 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.

Usually, this error occurs when you try to extract options into a shared file or when running 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() {
    // ...
  },
});