Before 2014, I had built a couple of web applications that had a zoomable user interface, ZUI. The experience made clear that we must have a separate software library to deal with many complexities of web ZUIs to allow the applications to be developed further. The complexities include, but unfortunately are not limited to, the scaling of HTML elements and dealing with browser viewport and native zoom gestures.
The lib received the name Taaspace, after the image canvas project Taataa from where most of the initial source code were adopted. The first web app to use the early versions of Taaspace was Solja, an effort to explore novel document browsing methods for Nokia Solutions and Networks.
Taaspace was later renamed to Tapspace.js. It is completely open source and free to use.
See the lib and try example apps at github.com/taataa/tapspace