Run npm start to show source locations in the error stack trace:
npm startError: not a number: x
at parse_age (.../src/app.cljs:6:14)
at <anonymous> (.../src/app.cljs:10:27)
...
at average_age (.../src/app.cljs:11:8)
Run npm run start:no-maps to compare with the compiled JavaScript locations.
Run npm run serve.
Open http://localhost:8137/examples/source-maps/ in your browser.
Open DevTools to view the error stack trace.