Here is everything you need to know about accessing 1.12 features in a web client.

The transition from 1.8 to 1.12 brought significant content additions to the browser port: Eaglercraft Download Eaglercraft Offline Clients

The original, most stable, and most popular version of Eaglercraft is based on (and partially 1.8.8). The creator (lax1dude) built it using JavaScript and WebGL to run inside a browser.

But let’s clear up a major point of confusion first.