Deciding to use Three.js naturally introduces a dependency into our web client application, but when it comes to 3D programming, it's a very acceptable trade-off. One can think of it as the jQuery for 3D graphics, providing invaluable utilities and shortcuts for common tasks, while greatly enhancing fallback capabilities and smoothing over differences in implementations. LeapJS is naturally pretty useful as well for our purposes.
Let's take a look at combining the two. We can either download the Three.js library and include it locally, or we can link to the latest build hosted by GitHub (or elsewhere). While linking to the latest build is great, because we get the latest optimizations and bug fixes without doing any work at all, downloading the library is usually a better option; development is a tad faster (page reloads are slightly quicker without having to fetch the file from GitHub, especially if you are not geographically proximate to their servers...