From Apple’s introduction:
The new LivePhotosKit JS API is available on NPM with code samples shared in the new API reference. In the new documentation, Apple includes examples on how to get Live Photo assets up and running online.
According to the official documentation:
Tumblr brought Live Photos to the web last year, and had even shared their own code implementations as well. Their work may have been what inspired Apple to eventually build out their own API for developers.