# Browser (/docs/browser)



In the browser there is no filesystem and no `process.env`. Your bundler inlines configuration at build time, and you seed a `PortableSource` from it, then read with the same typed API as everywhere else.

Import from `envapt`. The package export conditions resolve a node-free portable build in the browser automatically, so the same import works in local dev and in the bundle.

<Callout type="info">
  The filesystem-only config APIs have nothing to do in the browser, so they warn and no-op by default. Readers work as normal. See [Compatibility](/docs/compatibility) for `fileApiMode` and [Errors](/docs/errors) for the codes.

  ```ts twoslash
  import { Envapter } from 'envapt';

  Envapter.getBoolean('FEATURE_BETA', false); // readers work
  Envapter.baseDir = '/tmp'; // warns once and no-ops in the browser
  ```
</Callout>

## Seed from your bundler [#seed-from-your-bundler]

Bundlers replace build-time env references with string literals: Vite exposes them on `import.meta.env`, webpack through `DefinePlugin`. Pass that object to `PortableSource`, then read the values typed.

```ts
import { Envapter, PortableSource, Converters } from 'envapt';

Envapter.useSource(new PortableSource(import.meta.env));

const apiUrl = Envapter.getUsing('VITE_API_URL', Converters.Url); // URL, not a raw string
const beta = Envapter.getBoolean('VITE_ENABLE_BETA', false); // boolean
```

`import.meta.env.VITE_API_URL` is a string; `Envapter.getUsing('VITE_API_URL', Converters.Url)` returns a `URL`, and `getBoolean` returns a `boolean`. `PortableSource` snapshots the object and JSON-stringifies non-string values, so you can read Vite's boolean `DEV` and `PROD` flags too.

<Callout type="warn">
  Anything you seed into a browser `PortableSource` ships in your client bundle. Pass public configuration only,
  never a secret or a server-side key.
</Callout>

## Environment detection [#environment-detection]

`Envapter.environment` and the `isProduction` / `isDevelopment` / `isTest` helpers also read `MODE`, which Vite sets to `development`, `production`, or your `--mode` value. Because you bind `import.meta.env`, they work with no extra wiring. See [Environment](/docs/environment).

## No filesystem [#no-filesystem]

`PortableSource` snapshots its object at construction, so mutating that object afterward does not change what envapt reads. There is no `.env` cascade in the browser, and reading before you bind a source throws `NoSourceBound`. See [Sources](/docs/sources).

## Decorators [#decorators]

The default `@Envapt` accessor decorators work in the browser build, the legacy `envapt/legacy` form needs a compile step.

For the providers and the contract see [Sources](/docs/sources).