---
title: "@Import Annotation"
description: How to import platform-specific libraries in shared components.
---

---

Jaspr components can be rendered both on the server and client. The same code will be compiled twice for the server and
the web platform. Most of the time this isn't an issue, however sometimes you might want to use a package or library that
is only supported on one side, e.g.:

- `dart:html` is only supported on the client,
- `dart:io` is only supported on the server.

When you want to use such a library in your project, you would have to resort to *conditional imports*, 
which are quite cumbersome to use since you have to create multiple files and stub everything you want to use.

Jaspr can do this for you using the `@Import` annotation. Say you have the following component:

```dart title="lib/app.dart"
import 'dart:html' show window;

import 'package:jaspr/jaspr.dart';

class App extends StatelessComponent {
  @override
  Iterable<Component> build(BuildContext context) sync* {
    if (kIsWeb) {
      window.alert('Hi Jaspr');
    }
    yield p([text('Hello World')]);
  }
}
```

This component wants to show an alert when being built, but only on web. We can correctly use the `kIsWeb`
constant to check the platform **during runtime**, but this example would still lead to a 
**compile time error** when running on the server - because `dart:html` is unsupported there.

With Jasprs **platform-specific imports** you can change the code to this:

```dart title="lib/app.dart"
@Import.onWeb('dart:html', show: [#window])
import 'app.imports.dart';

import 'package:jaspr/jaspr.dart';

class App extends StatelessComponent {
  @override
  Iterable<Component> build(BuildContext context) sync* {
    if (kIsWeb) {
      window.alert('Hi Jaspr');
    }
    yield p([text('Hello World')]);
  }
}
```

This will:

- generate the `app.imports.dart` file
- setup conditional imports for `dart:html` on the web
- write stubs on the server for all imported members.

<Success>
There is a code-assist available from `jaspr_lints` that converts your imports automatically!
See [Linting](/get_started/linting).
</Success>
---

You can extend this to multiple imports and mix web and server imports like this:

```dart title="lib/app.dart"
@Import.onWeb('dart:html', show: [#window])
@Import.onWeb('package:some_package', show: [#someMember])
@Import.onServer('dart:io', show: [#Platform])
import 'app.imports.dart';
```

The `show` list must contain all the variables and types you want to access in your code, similar to
the `import ... show ...;` syntax. Here each item in the list must be a symbol starting with `#`.
