手动散布API是很危险的，我建议采取以下措施：
TaskBroker.prototype._connectMongo = Q.nfcall(MongoClient.connect, 'mongodb://127.0.0.1:27017/test',{});TaskBroker.prototype.connectMongo = function(){ return this._connectMongo().then(function(db){ console.log("Hello"); // self.stuff... return 42; }).catch(function(e){ console.err("connection error",e); // log the connection error, or handler err throw e; // don't mark as handled, propagate the error. });};有了Bluebird的承诺，它看起来就像：
var MongoClient = Promise.promisifyAll(require("mongodb").MongoClient);TaskBroker.prototype.connectMongo = function(){ return MongoClient.connectAsync().then(... // Bluebird will automatically track unhandled errors };
