Add environment variables docs (Closes #873) (#1587)

* Added environment variables docs (Closes #873)

* Fixed prefix

docs/src/config.ts

@@ -24,6 +24,7 @@ export const SIDEBAR = {
     { text: 'RSS', link: 'guides/rss' },
     { text: 'Supported Imports', link: 'guides/imports' },
     { text: 'Aliases', link: 'guides/aliases' },
+    { text: 'Environment Variables', link: 'guides/environment-variables' },
     { text: 'Deploy to the web', link: 'guides/deploy' },
     { text: 'Publish to npm', link: 'guides/publish-to-npm' },
 

docs/src/pages/guides/environment-variables.md

@@ -0,0 +1,29 @@
+---
+layout: ~/layouts/MainLayout.astro
+title: Using environment variables
+description: Learn how to use environment variables in an Astro project.
+---
+
+Astro uses Vite for environment variables, and allows you to use any of its methods to get and set environment variables. Note that all environment variables must be prefixed with `VITE_` to be accessible by client side code.
+
+## Setting environment variables
+
+Vite includes `dotenv` by default, allowing you to easily set environment variables with no configuration in Astro projects. You can also attach a mode (either `production` or `development`) to the filename, like `.env.production` or `.env.development`, which makes the environment variables only take effect in that mode.
+
+Just create a `.env` file in the project directory and add some variables to it.
+
+```bash
+# .env
+VITE_POKEAPI="https://pokeapi.co/api/v2"
+```
+
+## Getting environment variables
+
+Instead of using `process.env`, with Vite you use `import.meta.env`, which uses the `import.meta` feature added in ES2020 (don't worry about browser support though, Vite replaces all `import.meta.env` mentions with static values). For example, to get the `VITE_POKEAPI` environment variable, you could use `import.meta.env.VITE_POKEAPI`.
+
+```js
+fetch(`${import.meta.env.VITE_POKEAPI}/pokemon/squirtle`
+```
+
+> ⚠️WARNING⚠️:
+> Because Vite statically replaces `import.meta.env`, you cannot access it with dynamic keys like `import.meta.env[key]`.