Why the Project Structure of tutorial recommend is different from download the source code of “MyIonic2Project”

Why the recommend Project Structure of tutorial is different from download the source code of “MyIonic2Project”

for example
in the recommend Project Structure of tutorial,under source code was seeing up .
src=“build/js/app.bundle.js”

in the MyIonic2Project,is not setting up
under is the source of MyIonic2Project in the /www/ index.html
src="cordova.js"
src="build/polyfills.js"
src=“build/main.js”