Module parse failed: Unexpected token. react-native/index.js "typeof" operator

Question

I'm quite new to the front end - trying to implement client side on React. After adding "react-native" dependency and running webpack I'm getting the following error:

ERROR in ./node_modules/react-native/index.js 13:7
Module parse failed: Unexpected token (13:7)
You may need an appropriate loader to handle this file type, currently no loaders are configured to process this file. See https://webpack.js.org/concepts#loaders
| 'use strict';
| 
> import typeof AccessibilityInfo from './Libraries/Components/AccessibilityInfo/AccessibilityInfo';
| import typeof ActivityIndicator from './Libraries/Components/ActivityIndicator/ActivityIndicator';
| import typeof Button from './Libraries/Components/Button';
 @ ./node_modules/@react-navigation/native/lib/module/useBackButton.js 2:0-43 5:25-36
 @ ./node_modules/@react-navigation/native/lib/module/index.js
 @ ./src/main/js/app.js

I have the following dependencies in package.json:

 "dependencies": {
    "@react-native-community/masked-view": "^0.1.7",
    "@react-navigation/native": "^5.1.4",
    "@react-navigation/stack": "^5.2.9",
    "react": "^16.13.1",
    "react-dom": "^16.13.1",
    "react-native": "^0.62.1",
    "react-native-gesture-handler": "^1.6.1",
    "react-native-reanimated": "^1.7.1",
    "react-native-safe-area-context": "^0.7.3",
    "react-native-screens": "^2.4.0",
    "rest": "^2.0.0"
  },
  "scripts": {
    "watch": "webpack --watch -d"
  },
  "devDependencies": {
    "@babel/core": "^7.9.0",
    "@babel/preset-env": "^7.9.0",
    "@babel/preset-react": "^7.9.4",
    "babel-loader": "^8.1.0",
    "webpack": "^4.42.1",
    "webpack-cli": "^3.3.11"
  }

I assume that "typeof" operator is not recognized, but why?

Answer 1

Do you try to run React Native in the browser? If yes, I recommend using React Native for Web.

react-native can not run in the browser. You need to add an alias from react-native to react-native-web in webpack.config.js, so this package is used instead.

Following the React Native for Web documentation you need to make this modification to your webpack config:

// webpack.config.js
module.exports = {
    // ...the rest of your config

    resolve: {
        alias: {
            'react-native$': 'react-native-web'
        }
    }
}

Answer 2

I just spent a few hours dealing with this exact issue.

First, you can try adding "@babel/preset-flow" to your .babelrc file (after installing). That was recommended here, but didn't actually work for me.

What worked for me was just adding externals: { "react-native": true }, to my webpack.config.js file. My config file ended up looking like this:

const path = require("path")

module.exports = {
    entry: "./src/index.js",
    output: {
        filename: "main.js",
        path: path.resolve(__dirname, "dist"),
    },
    externals: {
        "react-native": true,
    },
    module: {
        rules: [
            {
                test: /\.(js|jsx)$/,
                exclude: /node_modules/,
                use: ["babel-loader"],
            },
            // ...
        ],
    },
}

My understanding is that react-native is a dependency, so @babel/preset-flow didn't actually get triggered to help interpret the flow formatting in those files - it may only handle files in the main "entry" location of your webpack.config.js file.

Hopefully this helps someone out there. Feel free to comment on this answer if I'm a bit off-base and I'll update this :)