cdn34 · July 17, 2018 10:26 · Apr 14, 2017 · Apr 14, 2017
diff --git a/node-modules-in-react-native.md b/node-modules-in-react-native.md
@@ -53,6 +53,8 @@ not a widely used approach and as long as Facebook uses React Native
 Packager internally, React Native will work best with React Native
 Packager.
 
+[rn webpack]: https://github.com/mjohnston/react-native-webpack-server
+
 ### rn-nodeify
 
 [rn-nodeify][] works by editing all `package.json` files in

diff --git a/node-modules-in-react-native.md b/node-modules-in-react-native.md
@@ -0,0 +1,127 @@
+# Running Node Modules in React Native
+
+*How to use packages that depend on Node.js core modules in React
+Native.*
+
+## Node.js Core Modules
+
+Node has several modules that are automatically available via
+`require()`: `http`, `crypto`, etc. While these modules are available
+in Node, they are not automatically available in other environments
+such as browsers and React Native.
+
+### Browsers
+
+"Node-style" code (using modules and `require()`) that targets browsers
+is usually compiled using tools such as Webpack or Browserify. These
+compilers implement `require()` and other functionality normally
+available in Node but not browsers, including [Node core modules
+implemented for browser usage][node-libs-browsers].
+
+[node-libs-browsers]: https://github.com/webpack/node-libs-browser
+
+### React Native
+
+Similar to the browsers scenario, React Native compiles "Node-style"
+code to run in the React Native environment via the [React Native
+Packager][]. The packager is similar to Webpack or Browserify, but with
+some minor differences, including having no official documentation or
+best practice for running Node core module.
+
+[react native packager]: https://github.com/facebook/react-native/tree/master/packager
+
+## Why
+
+Usually, there are React Native-specific counterparts to the Node core
+modules that provide the same functionality, e.g.,
+[react-native-crypto][]. So why does one need Node core modules to work
+in React Native? **The answer is cross-platform code and the vast npm
+ecosystem.** It's convenient to be able to use the same modules in React
+Native as in Node and browsers.
+
+[react-native-crypto]: https://github.com/mvayngrib/react-native-crypto
+
+## Prior Work
+
+There are several approaches to running Node core modules in React
+Native.
+
+### Webpack for React Native
+
+While it's possible to use [Webpack with React Native][rn webpack], it's
+not a widely used approach and as long as Facebook uses React Native
+Packager internally, React Native will work best with React Native
+Packager.
+
+### rn-nodeify
+
+[rn-nodeify][] works by editing all `package.json` files in
+`node_modules` to add the `react-native` field. Similar to the
+[`browser` field][browser field] in `package.json`, the `react-native`
+field tells the React Native Packager to substitute one modules with
+another (e.g., `crypto` with `react-native-crypto`). rn-nodeify also
+applies various other "hacks" to some sources files. See the [rn-nodeify
+readme][] for more information.
+
+This approach is less than ideal because it involves editing files in
+the `node_modules` directory and must be run after every time
+dependencies are changed.
+
+[rn-nodeify]: https://github.com/mvayngrib/rn-nodeify
+[rn-nodeify readme]: https://github.com/mvayngrib/rn-nodeify#what-it-does
+[browser field]: https://github.com/defunctzombie/package-browser-field-spec
+
+### ReactNativify
+
+[ReactNativify][] documents how to use a custom React Native Packager
+transformer and the [`babel-plugin-rewrite-require`][babel rewrite]
+Babel plugin to support Node core modules. While this solution is
+robust, being wholly encapsulated by the packager without depending on
+editing files in `node_modules`, it's not ideal as it involves
+maintaining a complicated [transformer implementation][] and keeping it
+up to date with [Packager's implementation][packager transformer].
+`babel-plugin-rewrite-require` also has slightly different behavior than
+Webpack and Browserify, not supporting `require()` calls with
+an expression (such as `require('cyrp' + 'to')`).
+
+[ReactNativify]: https://github.com/philikon/ReactNativify
+[transformer implementation]: https://github.com/philikon/ReactNativify/blob/master/transformer.js
+[packager's implementation]: https://github.com/facebook/react-native/blob/master/packager/transformer.js
+
+## `rn-cli.config.js` and `extraNodeModules`
+
+The best solution to running Node core modules in React Native is a
+built-in React Native Packager configuration option: `extraNodeModules`.
+This [little-known and undocumented feature][extraNodeModules] allows
+specifying modules that should be globally available as Node core
+modules. To use this configuration option, add a `rn-cli.config.js` file
+in the root directory of your React Native project:
+
+```js
+module.exports = {
+  extraNodeModules: {
+    crypto: require('react-native-cyrpto'),
+  },
+};
+```
+
+For extra convenience, you can use the [node-libs-browser][] package to
+make all modules available:
+
+```js
+module.exports = {
+  extraNodeModules: require('node-libs-browser'),
+};
+```
+
+[extraNodeModules]: https://github.com/facebookarchive/node-haste/pull/69
+
+## Global Environment
+
+While the above solution will make it possible to `require()` Node core
+modules, "Node-style" code also expects the global environment to be in
+a specific state. The React Native global environment should be mutated
+to meet these expectations. See [ReactNativify's `global.js`][global]
+for an example of doing this.
+
+[global]: https://github.com/philikon/ReactNativify/blob/master/global.js
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