[Fix error] An unhandled exception occurred: [BABEL] /workdir/test/chess/www/1-es2015.js: Could not find plugin "proposal-class-static-block" Error info How to fix this error This worked for me: Go to tsconfig.json change "target": "es2015", to "target": "es5", References https://forum.ionicframework.com/t/could-not-find-plugin-proposal-numeric-separator/185556/22