How are dynamic transitions achieved from a front end point of view

See for example the Google Accounts log-in experience, where you move from 'Enter email' to 'Enter password' via a smooth dynamic transition with no page refresh

https://accounts.google.com/

How can I speak to a front end designer about achieving this type of interaction? Is it just 'javascript'?

Too often I find developers turning UX specs for features like this into basic clunky page refreshes, and I want to have the language to speak to them about it

thanks