tern-threejs provides the threejs tern plugin which gives you a support for three.js.

After installing and converting your project as Tern Project, go at Tern project property, click on Tern / Modules item and select the three.js tern plugin (ECMAScript 6 and Browser tern plugin must be selected too) :

Completion

After that you can benefit with three.js completion :

Web Browser

You can play with online demo which uses CodeMirror (inside Web Browser).