Thanks! The aim for the chapter is indeed to show how ES6 and AngularJS simplify a typical web application like this.

The version at https://github.com/audreyt/500lines/tree/master/spreadsheet/... has exactly the same line count, but with more idiomatic workarounds that's less clear to students new to web development (the audience of this book).

It is possible to replace AngularJS (the only external library) with regular blur/focus/change handler as @xem shows — without affecting the line counts — but the separation of concerns between view, logic and worker would be less clear.