Achtung! This library is currently used in Atom and various Atom dependencies, but our long-term plan is to transition away from it in favor of the simpler event-kit library. Don't depend on supporting this library forever. Achtung Again! The Subscriber mixin requires ES6 Harmony WeakMaps. To enable them, run your program with the node --harmony_collections flag. If you're using it in a node framework such as jasmine, run its script with the flag enabled as follows: node --harmony-collections .bin/jasmine-node specs.