Today I put together a quick tutorial on how to build a 3d terrain in Javascript, from setting up three.js to loading a heightmap and texture. More will be added later (controls and collision).
Each step is organized as a release in the Github repo so you can download them all individually or browse through the commit diffs to see each change being made.
The Github project is here: https://github.com/wybiral/terrain
And, if course, there's a demo of it here: https://wybiral.github.io/terrain/