Ionic 2 error : build dev failed: Cannot read property 'indexOf' of undefined

I got error suddenly when running ionic 2 app

build dev failed: Cannot read property 'indexOf' of undefined 

Fix for the issue

Update the app-script to latest -> npm install @ionic/app-scripts@latest --save-dev
Change tsconfig.js -> compilerOptions insert "sourceMap": true, and remove lib option


Credits : https://github.com/driftyco/ionic-app-scripts/issues/597