framework/extensions/mentions/js/tsconfig.json

{
  // Use Flarum's tsconfig as a starting point
  "extends": "flarum-tsconfig",
  // This will match all .ts, .tsx, .d.ts, .js, .jsx files in your `src` folder
  // and also tells your Typescript server to read core's global typings for
  // access to `dayjs` and `$` in the global namespace.
  "include": ["src/**/*", "../vendor/flarum/core/js/dist-typings/@types/**/*"],
  "compilerOptions": {
    // This will output typings to `dist-typings`
    "declarationDir": "./dist-typings",
    "baseUrl": ".",
    "paths": {
      "flarum/*": ["../vendor/flarum/core/js/dist-typings/*"]
    }
  }
}