It&#x27;s perhaps not as custom as I made it sound. The code we have is a wrapper around the [virtual-dom](<a href="https:&#x2F;&#x2F;github.com&#x2F;Matt-Esch&#x2F;virtual-dom" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;Matt-Esch&#x2F;virtual-dom</a>) library which does most of the low level work.<p>The &quot;widget&quot; framework is a series of simple ES6 classes that allow us to keep state around and delegate events as actions up to Ember controllers. We had a lot of pre-existing, battle tested code that was written using Ember idioms and was not a performance problem, so we kept that around and used the virtual dom stuff just for rendering HTML as fast as possible.<p>Why not React? Our main pain point was rendering, and we didn&#x27;t need all the extra stuff React provided as those bases were already covered by Ember. Why include 26k min+gzip when we would only use a small part of it that was already provided by another excellent virtual-dom library?