Add docs about publicPath

Author: rafaelrinaldi

content/guides/public-path.md

@@ -0,0 +1,57 @@
+---
+title: Public Path
+sort: 14
+contributors:
+  - rafaelrinaldi
+---
+
+Webpack has a very useful configuration that let you specify the base path for
+all the assets on your application. It's called `publicPath`.
+
+## Use cases
+
+There are a few use cases on real applications where this feature becomes
+specially neat.
+
+### Set value on build time
+
+For development mode what we usually have is an `assets/` folder that lives on
+the same level of our index page. This is fine but let's say you want to host
+all these static assets on a CDN on your production environment?
+
+To approach this problem you can easily use a good old environment variable.
+Let's say we have a variable `ASSET_PATH`:
+
+```js
+import webpack from 'webpack';
+
+// Whatever comes as an environment variable, otherwise use root
+const ASSET_PATH = process.env.ASSET_PATH || '/';
+
+export default {
+  output: {
+    publicPath: ASSET_PATH
+  },
+
+  plugins: [
+    // This makes it possible for us to safely use env vars on our code
+    new webpack.DefinePlugin({
+      'process.env.ASSET_PATH': JSON.stringify(ASSET_PATH)
+    })
+  ]
+};
+```
+
+### Set value on the fly
+
+Another possible use case is to set the public path on the fly. Webpack exposes
+a global variable that let's you do that, it's called `__webpack_public_path__`.
+So in your application entry point, you can simply do this:
+
+```js
+__webpack_public_path__ = process.env.ASSET_PATH;
+```
+
+That's all you need. Since we're already using the `DefinePlugin` on our
+configuration, `process.env.ASSET_PATH` will always be defined so we can safely
+do that.