This paper introduces the JSAmbisonics library, a set of JavaScript modules based on the Web Audio API for spatial sound processing. Deployed via Node.js, the library consists of a compact set of tools for reproduction and manipulation of first-or higher-order recorded or simulated Ambisonic sound fields. After a brief introduction to the fundamentals of Ambisonic processing, the main components (encoding, rotation, beamforming, and binaural decoding) of the JSAmbisonics library are detailed. Each component , or " node " , can be used on its own or combined with others to support various application scenarios, discussed in Section 4. An additional library developed to support spherical harmonic transform operations is introduced in Section 3.2. Careful consideration has been given to the overall computational eciency of the JSAmbisonics library, particularly regarding spatial-encoding and decoding schemes, optimized for real-time production and delivery of immersive web contents.