Just an update, it turns out that Typed Arrays aren't as fast as node's Buffer implementation. When comparing msgpack-js-browser to the native JSON library, JSON is way faster in chrome. http://jsperf.com/msgpack-js-vs-json

However, in the number and array heavy case, the msgpack is 2.5x smaller when serialized. So even if it's a bit slower in browsers, the bandwidth savings and the ability to store binary data may still be worth it. (remember that performance in the browser scales very differently since it's distributed across all your client's browsers)