node.js中的events.EventEmitter.listenerCount方法使用说明_node.js

EventEmitter.listenerCount(emitter, event)

if(events.EventEmitter.listenerCount(this, 'feedback') == 0) {
//....
}

EventEmitter.listenerCount = function(emitter, type) {
var ret;
if (!emitter._events || !emitter._events[type])
ret = 0;
else if (util.isFunction(emitter._events[type]))
ret = 1;
else
ret = emitter._events[type].length;
return ret;
};