src/event.js
function addListener(event, callback, meta) {
  event.listeners.push(callback);
  event.meta.set(callback, meta);
}
function addListener(event, callback, meta) {
  event.listeners.push(callback);
  event.meta.set(callback, meta);
}
function addListener ( event , callback , meta ) { event . listeners . push ( callback ) ; event . meta . set ( callback , meta ) ; }
Adds listener to event

@param {Object} event
@param {Function} callback
@param {Object} meta
Adds listener to event