1. OS X - This guide assumes OS X which is needed for iOS development.
2. [Homebrew](http://brew.sh/) is the recommended way to install Watchman and Flow.
3. Install [Node.js](https://nodejs.org/) 4.0 or newer.
- Install **nvm** with [its setup instructions here](https://github.com/creationix/nvm#installation). Then run `nvm install node && nvm alias default node`, which installs the latest version of Node.js and sets up your terminal so you can run it by typing `node`. With nvm you can install multiple versions of Node.js and easily switch between them.
- New to [npm](https://docs.npmjs.com/)?
4.`brew install watchman`. We recommend installing [watchman](https://facebook.github.io/watchman/docs/install.html), otherwise you might hit a node file watching bug.
5.`brew install flow`, if you want to use [flow](http://www.flowtype.org).
To write React Native apps for Android, you will need to install the Android SDK (and an Android emulator if you want to work on your app without having to use a physical device). See [Android setup guide](docs/android-setup.html) for instructions on how to set up your Android environment.
- Open `index.android.js` in your text editor of choice and edit some lines.
- Press the menu button (F2/⌘-M by default, depending on AVD version, or ⌘-M in Genymotion) and select *Reload JS* (or press R twice) to see your change!
If you already have a (iOS-only) React Native project and want to add Android support, you need to execute the following commands in your existing project directory: