Summary
npx expo start --web fails to bundle on a clean install, before any application code is reached. The result is a blank page at localhost:8081.
Web Bundling failed 723ms index.js (3 modules)
ERROR SyntaxError: node_modules/expo/src/Expo.ts: Support for the experimental syntax 'flow' isn't currently enabled (26:8):
> 26 | export type {
| ^
Cause
frontend/ contains two Babel configs.
babel.config.js — correct for Expo:
module.exports = function (api) {
api.cache(true);
return {
presets: ['babel-preset-expo'],
};
};.babelrc — preset-env only:
{
"presets": [["@babel/preset-env", { "targets": { "node": "current" } }]]
}Babel gives .babelrc precedence for files inside its package root, so babel-preset-expo never loads. Without it there is no Flow support, and Expo's own Flow-typed source can't be parsed — the failure happens in node_modules, not in app code, which is why the error looks unrelated to anything in the repo.
Both files arrived together in #206. I suspect .babelrc was added so Jest could transform tests with preset-env, without it being obvious that it would also take priority over babel.config.js for the bundler.
Verified
Renaming .babelrc out of the way is sufficient:
Web Bundled 7555ms index.js (2505 modules)
and the app renders the login screen normally. With the file in place the bundle fails every time.
Impact
The web target doesn't run at all on a fresh clone.
That also explains how a missing navigation import reached main (#209): web-facing bugs can't be caught locally when the web build never starts. Anyone trying to reproduce #209 hits this first and sees a blank page rather than the reported ReferenceError.
Suggested fix
Remove .babelrc and give Jest its own transform configuration, so the two don't compete. babel-preset-expo handles both the bundler and tests when it's the only config in play.
Worth noting there's currently no jest.config.js and no jest key in package.json, so whatever .babelrc was solving needs re-solving deliberately rather than just deleted.
A separate but related problem
frontend/package.json declares:
"@babel/core": "^8.0.1",
"@babel/preset-env": "^8.0.2",
while expo ~56.0.4 requires Babel 7. npm install prints fifteen ERESOLVE warnings, all of the form peer @babel/core@"^7.0.0-0".
This is not the cause of the bundling failure — I tested with Babel 7 pinned and the identical error appeared, which is what led me to the .babelrc shadowing. But it should be reconciled in the same pass, since it's the kind of mismatch that produces confusing failures later.
Happy to take this if it's free.
Summary
npx expo start --webfails to bundle on a clean install, before any application code is reached. The result is a blank page atlocalhost:8081.Cause
frontend/contains two Babel configs.babel.config.js— correct for Expo:.babelrc— preset-env only:{ "presets": [["@babel/preset-env", { "targets": { "node": "current" } }]] }Babel gives
.babelrcprecedence for files inside its package root, sobabel-preset-exponever loads. Without it there is no Flow support, and Expo's own Flow-typed source can't be parsed — the failure happens innode_modules, not in app code, which is why the error looks unrelated to anything in the repo.Both files arrived together in #206. I suspect
.babelrcwas added so Jest could transform tests withpreset-env, without it being obvious that it would also take priority overbabel.config.jsfor the bundler.Verified
Renaming
.babelrcout of the way is sufficient:and the app renders the login screen normally. With the file in place the bundle fails every time.
Impact
The web target doesn't run at all on a fresh clone.
That also explains how a missing navigation import reached
main(#209): web-facing bugs can't be caught locally when the web build never starts. Anyone trying to reproduce #209 hits this first and sees a blank page rather than the reportedReferenceError.Suggested fix
Remove
.babelrcand give Jest its own transform configuration, so the two don't compete.babel-preset-expohandles both the bundler and tests when it's the only config in play.Worth noting there's currently no
jest.config.jsand nojestkey inpackage.json, so whatever.babelrcwas solving needs re-solving deliberately rather than just deleted.A separate but related problem
frontend/package.jsondeclares:while
expo ~56.0.4requires Babel 7.npm installprints fifteenERESOLVEwarnings, all of the formpeer @babel/core@"^7.0.0-0".This is not the cause of the bundling failure — I tested with Babel 7 pinned and the identical error appeared, which is what led me to the
.babelrcshadowing. But it should be reconciled in the same pass, since it's the kind of mismatch that produces confusing failures later.Happy to take this if it's free.