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docs: add import.meta.env.DEV examples #20352

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25 changes: 25 additions & 0 deletions docs/guide/env-and-mode.md
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Expand Up @@ -16,6 +16,31 @@ Some built-in constants are available in all cases:

- **`import.meta.env.SSR`**: {boolean} whether the app is running in the [server](./ssr.md#conditional-logic).

## Conditional Compilation
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I don't think we need a whole section for this. I think a simple example is enough.

:::details Example
```js
if (import.meta.env.DEV) {
  // code inside here will be treeshaken
  console.log('Dev mode') 
}
```
:::


You can include code only in certain modes (for example, only in development, not in production) by wrapping it in conditionals based on Vite's `import.meta.env` values.

For example:

```js
if (import.meta.env.DEV) {
// This code will only run when import.meta.env.DEV is true (in development mode).
console.log('Dev mode only!');
}
```

This is especially useful for including debugging tools or logs only during development, or for excluding code from your production build.

Similarly, you can use `import.meta.env.PROD` for production-only code:

```js
if (import.meta.env.PROD) {
// This code will only run in production mode.
}
```

The conditionals are statically replaced at build time, so code that is only meant for development will not be included in your production bundle, allowing for effective tree-shaking and smaller builds.

## Env Variables

Vite exposes env variables under `import.meta.env` object as strings automatically.
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