You can install the module directly from npm registry:
npm install otr4-em
A short tutorial is available.
Latest API documentation can be found here
For version's older than v0.1.0 see documentation here
The module is dual licensed: GPLv2 and LGPL You may choose the license that is more suitable for your application.
Important Note: The package includes an optimised/minified precompiled libotr4.js to simplify npm package installation. You may rebuild libotr4.js from source if required. How-to build libotr4.js