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Callstack Engineers
Callstack Engineers

Posted on • Edited on • Originally published at callstack.com

Setting up React Native Monorepo with Yarn Workspaces

#reactnative #appdevelopment #monorepo #guide

by Oskar Kwaśniewski

What is a monorepo?

A monorepo is a single repository that holds a multitude of projects with all their code and assets. While the projects can be related, they can be used independently by different teams.

Working with monorepos is very useful, especially when developing big and complex applications like super apps. Monorepos enable sharing the logic between a web app and a mobile app, for example.

In this article, we’re going to set up a basic structure for a monorepo in React Native.

Why use monorepo in React Native?

Thanks to react-native-web we can share every component so there’s no need to duplicate the code many times. This means easier dependency management, shorter CI times, and better collaboration between teams since the code can be shared.

The main advantage though is the possibility of sharing packages between React and React Native. Most of the time we decide to share only business logic, but thanks to React Native Web, we can also share some of the UI components.

Setting up Yarn workspaces

While setting up a monorepo, we have two options: we can either hoist the packages to the root level or prevent them from hoisting. Yarn workspaces have an option named nohoist which allows us to specify packages that aren’t hoisted. It depends on your use case but most of the time it’s better to hoist packages to the root level.

Alternatively, you can use npm workspaces, it should work the same.

Why it’s better to avoid using nohoist

Preventing packages from hoisting takes back the main advantage of monorepos which is sharing node_modules between repositories. When nohoist option is turned on, most of the time packages are duplicated inside the root level node_modules and inside the project level node_modules. Downloading packages multiple times can lead to longer CI/CD runs and higher costs.

Rearranging the project structure

In order to set up yarn workspaces, we need to restructure our project to suit the structure below. Projects need to be divided into separate folders and we should have root level package.json.

your-project
    packages
        web // <- React app
        mobile // <- React Native app
        shared // <- Shared (includes files shared between mobile/web)
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plain1.txt hosted with ❤ by GitHub

Next, you should create a package.json file in the root directory of our project with this command: $ yarn init -y

It should look like this:

{
  "private": "true",
  "name": "example-app",
  "version": "1.0.0",
  "workspaces": [
    "packages/*"
  ]
}
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codesnippet1.json hosted with ❤ by GitHub

Note that private: true is required because workspaces are not meant to be published.

In the workspaces section, we define a work tree. We can pass there an array of glob patterns that should be used to locate the workspaces. So in the example above, every folder inside packages is defined as a workspace.

Creating a React Native project

Use command below to create a React Native project inside the packages folder:

$ npx react-native init ExampleApp --directory mobile --template react-native-template-typescript
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plain2.txt hosted with ❤ by GitHub

In order for our app to work in a monorepo structure, we need to make sure that config files are pointing to the root level node_modules due to package hoisting.

iOS setup 

Change paths at the top of your Podfile
- require_relative '../node_modules/react-native/scripts/react_native_pods'
- require_relative '../node_modules/@react-native-community/cli-platform-ios/native_modules'
+ require_relative '../../../node_modules/react-native/scripts/react_native_pods'
+ require_relative '../../../node_modules/@react-native-community/cli-platform-ios/native_modules'

target 'ExampleApp' do
...
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path1.diff hosted with ❤ by GitHub

Regenerate Pods, by entering the command below in the packages/mobile folder:

$ cd ios && pod install
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plain3.txt hosted with ❤ by GitHub

Next open Xcode and inside Project settings > Build Phases open “Bundle React Native code and images”

Change the path of the script:

set -e

- WITH_ENVIRONMENT="../../node_modules/react-native/scripts/xcode/with-environment.sh"
- REACT_NATIVE_XCODE="../../node_modules/react-native/scripts/react-native-xcode.sh"
+ WITH_ENVIRONMENT="../../../node_modules/react-native/scripts/xcode/with-environment.sh"
+ REACT_NATIVE_XCODE="../../../node_modules/react-native/scripts/react-native-xcode.sh"

/bin/sh -c "$WITH_ENVIRONMENT $REACT_NATIVE_XCODE"
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path2.diff hosted with ❤ by GitHub

It should look like this:

Image description

Android setup

React Native ≥ 0.71

Uncomment the line with reactNativeDir and point it to root node_modules

// packages/mobile/android/app/build.gradle

react { 
+  hermesCommand = "../../node_modules/react-native/sdks/hermesc/%OS-BIN%/hermesc"
}
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android 1.diff hosted with ❤ by GitHub

In top-level build.gradle add this:

allprojects {
    project.pluginManager.withPlugin("com.facebook.react") {
        react {
            reactNativeDir = rootProject.file("../../../node_modules/react-native/")
            codegenDir = rootProject.file("../../../node_modules/react-native-codegen/")
        }
    }
}
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android 2.shell hosted with ❤ by GitHub

and inside: packages/mobile/android/settings.gradle

+ apply from: file("../../../node_modules/@react-native-community/cli-platform-android/native_modules.gradle"); applyNativeModulesSettingsGradle(settings)
+ includeBuild('../../../node_modules/react-native-gradle-plugin')
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android 3.diff hosted with ❤ by GitHub
‍
React Native ≤ 0.71

Fix paths inside packages/mobile/android/build.gradle
Change url of the React Native Android binaries, and Android JSC in the allprojects section:

allprojects {
    repositories {
        maven {
            // All of React Native (JS, Obj-C sources, Android binaries) is installed from npm
-            url("$rootDir/../node_modules/react-native/android")
+            url("$rootDir../../../../node_modules/react-native/android")
        }
        maven {
            // Android JSC is installed from npm
-            url("$rootDir/../node_modules/jsc-android/dist")
+            url("$rootDir../../../../node_modules/jsc-android/dist")
        }
                ...
    }
}
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code snippet2.diff hosted with ❤ by GitHub

Fix packages/mobile/android/settings.gradle
Here we also need to change paths to the root node_modules folder.

rootProject.name = 'example-app'
- apply from: file("../node_modules/@react-native-community/cli-platform-android/native_modules.gradle"); applyNativeModulesSettingsGradle(settings)
- includeBuild('../node_modules/react-native-gradle-plugin')
+ apply from: file("../../../node_modules/@react-native-community/cli-platform-android/native_modules.gradle"); applyNativeModulesSettingsGradle(settings)
+ includeBuild('../../../node_modules/react-native-gradle-plugin')
include ':app'
if (settings.hasProperty("newArchEnabled") && settings.newArchEnabled == "true") {
    include(":ReactAndroid")
-   project(":ReactAndroid").projectDir = file('../node_modules/react-native/ReactAndroid')
+   project(":ReactAndroid").projectDir = file('../../../node_modules/react-native/ReactAndroid')
    include(":ReactAndroid:hermes-engine")
-   project(":ReactAndroid:hermes-engine").projectDir = file('../node_modules/react-native/ReactAndroid/hermes-engine')
+   project(":ReactAndroid:hermes-engine").projectDir = file('../../../node_modules/react-native/ReactAndroid/hermes-engine')
}
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path3.diff hosted with ❤ by GitHub

Next go to packages/mobile/android/app/build.gradle
Inside the project.ext.react we need to add property cliPath so it will override the default location of the cli.

project.ext.react = [
+    cliPath: "../../../../node_modules/react-native/cli.js",
]
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plain4.txt hosted with ❤ by GitHub

In the same file, change this line: apply from: "../../node_modules/react-native/react.gradle" to point to root level node_modules as well.

- apply from: "../../node_modules/react-native/react.gradle"
+ apply from: "../../../../node_modules/react-native/react.gradle"
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path4.diff hosted with ❤ by GitHub

And also change: inside packages/mobile/android/app/build.gradle

- apply from: file("../../node_modules/@react-native-community/cli-platform-android/native_modules.gradle"); applyNativeModulesAppBuildGradle(project)
+ apply from: file("../../../../node_modules/@react-native-community/cli-platform-android/native_modules.gradle"); applyNativeModulesAppBuildGradle(project)
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path5.diff hosted with ❤ by GitHub

If you are using or planning to use the new architecture, we also need to change a few lines in the isNewArchitectureEnabled() if statement*.*

if (isNewArchitectureEnabled()) {
            // We configure the NDK build only if you decide to opt-in for the New Architecture.
            externalNativeBuild {
                ndkBuild {
                    arguments "APP_PLATFORM=android-21",
                        "APP_STL=c++_shared",
                        "NDK_TOOLCHAIN_VERSION=clang",
                        "GENERATED_SRC_DIR=$buildDir/generated/source",
                        "PROJECT_BUILD_DIR=$buildDir",
-                       "REACT_ANDROID_DIR=$rootDir/../node_modules/react-native/ReactAndroid",
-                       "REACT_ANDROID_BUILD_DIR=$rootDir/../node_modules/react-native/ReactAndroid/build",
-                       "NODE_MODULES_DIR=$rootDir/../node_modules"
+                       "REACT_ANDROID_DIR=../../node_modules/react-native/ReactAndroid",
+                       "REACT_ANDROID_BUILD_DIR=../../node_modules/react-native/ReactAndroid/build",
+                       "NODE_MODULES_DIR=../../node_modules"
                    cFlags "-Wall", "-Werror", "-fexceptions", "-frtti", "-DWITH_INSPECTOR=1"
                    cppFlags "-std=c++17"
                    // Make sure this target name is the same you specify inside the
                    // src/main/jni/Android.mk file for the `LOCAL_MODULE` variable.
                    targets "okwasniewskionboarding_appmodules"
                }
            }
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code snippet 3.diff hosted with ❤ by GitHub

Configure Metro

We’re almost done with setting up the project. The last thing in the React Native app is to add watchFolders so metro knows where the linked node_modules are. The shared modules are symlinked by yarn, and since metro doesn’t follow symlinks we need to explicitly say it where the linked node_modules are.

const path = require("path");

// packages/mobile/metro.config.js
module.exports = {
  watchFolders: [
    path.resolve(__dirname, '../../node_modules')
  ],
};
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code snippet4.javascript hosted with ❤ by GitHub

Setting up a shared package

To keep it simple, we’re going to share only one function across React Native and React.

Inside the packages/shared, create a new package.json file with the command:

$ yarn init -y
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code snippet5.javascript hosted with ❤ by GitHub

The shared library is in typescript, so we need to set up a build step with the typescript compiler (tsc).

The build step uses rimraf which is a small utility for node that allows us to remove a folder, and then build the app with tsc.

postinstall indicates that our shared dependency will build automatically after installing.

{
  "name": "@example-app/shared",
  "version": "1.0.0",
  "main": "dist/index.js",
  "scripts": {
    "build": "rimraf dist && tsc",
    "postinstall": "yarn build",
        "watch": "tsc --watch"
  },
    "dependencies": {
        "react-native": "0.69.1",
        "react": "18.0.0"
    },
    "devDependencies": {
        "rimraf": "^3.0.2",
        "typescript": "^4.4.4"
    },
  "keywords": [],
  "author": "",
  "license": "ISC"
}
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code snippet6.json hosted with ❤ by GitHub

Note: The package name is really important, because it will indicate from where we will import our module.

It’s also important to add all packages and keep the exact same version used in a shared project and target projects.

Next we need to configure tsconfig.json where we can define our build settings.

Here is an example config file:

// packages/shared/tsconfig.json
{
    "compilerOptions": {
      "target": "es6",
      "lib": ["dom", "dom.iterable", "esnext"],
      "skipLibCheck": true,
      "esModuleInterop": true,
      "allowSyntheticDefaultImports": true,
      "strict": true,
      "forceConsistentCasingInFileNames": true,
      "module": "commonjs",
      "outDir": "dist", // <- Directory of generated output
      "moduleResolution": "node",
      "resolveJsonModule": true,
      "experimentalDecorators": true,
      "strictPropertyInitialization": false,
      "declaration": true,
      "jsx": "react"
    },
  }
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code snippet7.json hosted with ❤ by GitHub

Next, let’s create an index.ts file inside the packages/shared folder.

export const add = (a: number, b: number) => {
    return a + b;
}
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code snippet8.javascript hosted with ❤ by GitHub

Run this command to build the package:

$ yarn build
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code snippet9.javascript hosted with ❤ by GitHub

Next, we need to add this package as a dependency in our react native project. So inside packages/mobile/package.json add @example-app/shared as a dependency.

Note that the version of the package must match the version specified inside packages/shared/package.json. Previously we defined that @example-app/shared version is 1.0.0.

// packages/mobile/package.json

"dependencies": {
    "@example-app/shared": "1.0.0",
    ...
  },
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code snippet10.json hosted with ❤ by GitHub

And also inside the metro.config.js

// packages/mobile/metro.config.js

module.exports = {
  watchFolders: [
    path.resolve(__dirname, '../../node_modules'),
+   path.resolve(__dirname, '../../node_modules/@example-app/shared'),
  ],
};
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code snippet11.javascript hosted with ❤ by GitHub

Now, run this command in the root directory, so yarn will set up symlinks for your shared package.

$ yarn
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code snippet12.javascript hosted with ❤ by GitHub

Right now we should be able to import the add function inside React Native app.

import React from 'react';
import {Text, TouchableOpacity, View} from 'react-native';
import {add} from '@example-app/shared';


const App = () => {
  return (
    <View>
      <TouchableOpacity
        accessibilityRole="button"
        onPress={() => {
          console.log(add(1, 2));
        }}>
        <Text>Run Add function</Text>
      </TouchableOpacity>
    </View>
  );
};

export default App;
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code snippet13.javascript hosted with ❤ by GitHub

Setting up a React project

In order to set up a React project, execute the command below inside packages/web:

$ npx create-react-app . ExampleApp --template typescript
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code snippet14.javascript hosted with ❤ by GitHub

Add @example-app/shared dependency:

// packages/web/package.json
"dependencies": {
    "@example-app/shared": "1.0.0",
    ...
  },
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code snippet15.json hosted with ❤ by GitHub

And we can import and use the shared package:

import React from 'react';
import {add} from '@example-app/shared';


const App = () => {
  return (
    <div>
      <button onClick={() => console.log(add(1,2))}>Run add function</button>
    </div>
  );
};

export default App;
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code snippet16.javascript hosted with ❤ by GitHub

Sharing UI components with React Native Web

In order to share UI components, we need React Native Web which provides a compatibility layer between React DOM and React Native.

Installation steps

Install react-native-web:

$ yarn add react-native-web
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code snippet17.txt hosted with ❤ by GitHub

Install babel-plugin-react-native-web

$ yarn add -D babel-plugin-react-native-web
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code snippet18.txt hosted with ❤ by GitHub

Modify shared package to export React Native component

First inside packages/shared, create a new file called TestComponent.tsx

import { Text, View } from "react-native";
import React from "react";

const TestComponent = () => {
  return (
    <View>
      <Text>TestComponent</Text>
    </View>
  );
};

export default TestComponent;
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code snippet 19.javascript hosted with ❤ by GitHub

Next export it from the index.ts file:

export const add = (a: number, b: number) => {
    return a + b;
}

export { default as TestComponent } from './TestComponent.tsx'
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code snippet20.javascript hosted with ❤ by GitHub

Rebuild the shared package inside packages/shared folder:

$ yarn build
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code snippet21.txt hosted with ❤ by GitHub

And now we should be able to use TestComponent inside a React app.

import React from 'react';
import {add, TestComponent} from '@example-app/shared';


const App = () => {
  return (
    <div>
      <button onPress={() => console.log(add(1,2))}>Run add function</button>
            <TestComponent/> // <- React Native component inside React app! 
    </div>
  );
};

export default App;
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code snippet22.javascript hosted with ❤ by GitHub

To sum up

Setting up a monorepo can be tricky, but it pays off in the long run! You can easily share all of your code and assets between React and React Native.

Using a monorepo is growing in popularity - there is even an open proposal to migrate react-native repository to monorepo. Find out more about React Native monorepo on github.

This article was originally published at callstack.com on October 11, 2022.

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