It's just like if you wanted some-datepicker.js which depended on jquery1.1 but the rest of your code was jquery1.8 Polymer suffers from this because they are

It's just like if you wanted some-datepicker.js which depended on jquery1.1 but the rest of your code was jquery1.8 Polymer suffers from this because they are registering global custom element - just like when jquery registered itself as global $ React components does not register themselves anywhere so this problem does not exists at all. It doesnt matter for google simply because they are not using anything else outside of google and everything is running from master, they really have one big "git-like" repository with all their projects and everything is always up-to-date (and it's a lot of work to not break anything) You probably know HotReload already - it refreshes the browser if you make any change. HMR (hot module replacement) is one step further, it will update the page without refreshing - so forexample you can click the button, and then make changes in modal, and those will get re-rendered - it is also possible to retain form-state... P.S. Czech, Brno :)