Metro bundler failing to build "Failed to construct transformer" in Expo

Question

I am attempting to build a release version of my React Expo Bare Workflow iOS application and when I run the command npx expo run:ios --configuration Release or build through Xcode, I get the following error:

Failed to construct transformer:  /Users/{USER}/Documents/Projects/sentiance-expo/node_modules/@expo/metro-config/build/transform-worker/asset-transformer.js:21
    options ??= options || {
            ^^^

SyntaxError: Unexpected token '??='
...

My package.json

{
  "name": "sentiance-expo",
  "version": "1.0.0",
  "main": "expo-router/entry",
  "scripts": {
    "start": "expo start --dev-client",
    "android": "expo run:android",
    "ios": "expo run:ios",
    "web": "expo start --web"
  },
  "dependencies": {
    "@apollo/client": "^3.9.4",
    "@babel/runtime": "^7.23.9",
    "@mapbox/polyline": "^1.2.1",
    "@react-navigation/drawer": "^6.6.7",
    "@sentiance-react-native/core": "^6.6.0",
    "@sentiance-react-native/event-timeline": "^6.6.0",
    "@types/react": "~18.2.45",
    "axios": "^1.6.7",
    "expo": "^50.0.0",
    "expo-clipboard": "~5.0.1",
    "expo-constants": "~15.4.5",
    "expo-dev-client": "~3.3.8",
    "expo-device": "~5.9.3",
    "expo-linking": "~6.2.2",
    "expo-location": "~16.5.3",
    "expo-router": "~3.4.7",
    "expo-sensors": "~12.9.1",
    "expo-splash-screen": "~0.26.4",
    "expo-status-bar": "~1.11.1",
    "graphql": "^15.8.0",
    "react": "18.2.0",
    "react-native": "0.73.4",
    "react-native-circular-progress": "^1.3.9",
    "react-native-device-info": "^10.12.0",
    "react-native-gesture-handler": "~2.14.0",
    "react-native-maps": "1.10.0",
    "react-native-permissions": "^3.3.1",
    "react-native-reanimated": "~3.6.2",
    "react-native-safe-area-context": "4.8.2",
    "react-native-screens": "~3.29.0",
    "react-native-svg": "^14.1.0"
  },
  "devDependencies": {
    "@babel/core": "^7.20.0",
    "@babel/preset-env": "^7.23.9",
    "@types/mapbox__polyline": "^1.0.5",
    "@types/progressbar.js": "^1.1.7",
    "eslint": "^8.56.0",
    "typescript": "^5.3.3"
  },
  "private": true
}

babel.config.js

module.exports = function (api) {
  api.cache(true);
  return {
    presets: ["babel-preset-expo"],
    plugins: ["react-native-reanimated/plugin"],
  };
};

Things I've tried:

• Deleting package-lock.json, node modules, pods, podfile.lock and reinstalling all of them
• Deleting and rebuilding iOS build folder
• Attempted to downgrade to lowest Node version (v18)
• export NODE_OPTIONS=--openssl-legacy-provider in terminal
• npx expo install --fix this was a fresh project so there wasn't anything
• npx expo-doctor

I am able to run this app both in android and iOS in their emulators so I can confirm that the app does indeed work.

Further stacktrace:

error: Cannot read property 'transformFile' of undefined
TypeError: Cannot read property 'transformFile' of undefined
TypeError: Cannot read property 'transformFile' of undefined
    at Bundler.transformFile (/Users/[USER]/Documents/Projects/sentiance-expo/node_modules/metro/src/Bundler.js:43:30)
    at async Object.transform (/Users/[USER]/Documents/Projects/sentiance-expo/node_modules/metro/src/lib/transformHelpers.js:130:12)
    at async transform (/Users/[USER]/Documents/Projects/sentiance-expo/node_modules/metro/src/DeltaBundler/Graph.js:164:26)
    at async visit (/Users/[USER]/Documents/Projects/sentiance-expo/node_modules/metro/src/DeltaBundler/buildSubgraph.js:82:29)
    at async Promise.all (index 0)
    at async buildSubgraph (/Users/[USER]/Documents/Projects/sentiance-expo/node_modules/metro/src/DeltaBundler/buildSubgraph.js:103:3)
    at async Graph._buildDelta (/Users/[USER]/Documents/Projects/sentiance-expo/node_modules/metro/src/DeltaBundler/Graph.js:157:22)
    at async Graph.initialTraverseDependencies (/Users/[USER]/Documents/Projects/sentiance-expo/node_modules/metro/src/DeltaBundler/Graph.js:140:19)
    at async DeltaCalculator._getChangedDependencies (/Users/[USER]/Documents/Projects/sentiance-expo/node_modules/metro/src/DeltaBundler/DeltaCalculator.js:151:25)
    at async DeltaCalculator.getDelta (/Users/[USER]/Documents/Projects/sentiance-expo/node_modules/metro/src/DeltaBundler/DeltaCalculator.js:68:16)

Answer 1

What node version are you running?

node -v

The ??= syntax is only supported in Node 15 and higher.