chore: add webpack guides

guides/webpack.md

@@ -0,0 +1,71 @@
+---
+title: Webpack
+stack: Bundler
+description: Update webpack to output ES Modules
+---
+
+webpack is one of the early bundlers for the JavaScript ecosystem. Currently, support for ESM-format outputs is still under `experiments`
+
+## 1. Mark the package as ESM
+
+Add `type: "module"` to your `package.json`. Every `.js` file in the package is
+now treated as an ES module.
+
+```json
+{
+	"name": "my-package",
+	"type": "module"
+}
+```
+
+Any file that genuinely still has to be CommonJS (for example, a legacy config
+file for another tool) can keep the `.cjs` extension.
+
+## 2. Emit a single ESM bundle
+
+In webpack 5, enable module output and set the library to `module`:
+
+```js
+export default {
+	mode: 'production',
+	entry: './src/index.js',
+	experiments: {
+		outputModule: true
+	},
+	output: {
+		filename: 'index.js',
+		module: true,
+		library: {
+			type: 'module'
+		},
+		chunkFormat: 'module'
+	}
+};
+```
+
+If you had a separate CommonJS build, remove it and keep just the ESM output.
+For config files that must stay CommonJS, rename them to `.cjs` instead of `.js`.
+
+## 3. Point `exports` at the bundle
+
+Replace `main` with an `exports` field. This is what lets Node.js and bundlers
+resolve your package, and it stops deep imports into your `dist` folder from
+becoming part of your public API by accident.
+
+```json
+{
+	"exports": {
+		".": "./dist/index.js"
+	},
+	"files": ["dist"]
+}
+```
+
+## 4. Check the result
+
+Run [publint](https://publint.dev) to catch problems with leftover CommonJS
+references, publishing config, and other package metadata issues.
+
+```sh
+npx publint
+```