在My Alexa Lambda node js中将数据发布到MQTT broker后出现错误承诺

Question

我的Lambda有问题，实际上是在promise nodejs中。我在我的Lambda:中写了这样的代码

'use strict'
const Alexa = require('alexa-sdk');
const mqtt = require('mqtt');
const APP_ID = undefined;
const WELCOME_MESSAGE = 'Welcome to the lamp control mode';
const WELCOME_REPROMT = 'If you new please say help'
const HELP_MESSAGE = 'In this skill you can controlling lamp to turn off or on, dim the lamp, change the lamp color and schedule the lamp';
const STOP_MESSAGE = 'Thanks for using this skill, Goodbye!';
const OFF_RESPONSE = 'Turning off the lamp';
const ON_RESPONSE = 'Turning on the lamp';
const DIM_RESPONSE = 'Dimming the lamp';
const CHANGE_RESPONSE = 'Changing the lamp color';
const AFTER_RESPONSE = 'Wanna control something again ?';
const handlers = {
'LaunchRequest': function () {
this.emit(':ask', WELCOME_MESSAGE, WELCOME_REPROMT);
},
'OnOffIntent' : function () {
var status = this.event.request.intent.slots.status.value;
var location = this.event.request.intent.slots.location.value;
console.log(status);
console.log(location);
if (status == 'on') {
// Promise Start
var mqttPromise = new Promise(function(resolve, reject) {
var options = {
port: '1883',
clientId: 'mqttjs_' + Math.random().toString(16).substr(2, 8),
username: 'username',
password: 'password',
};
var client  = mqtt.connect('mqtt://broker-address', options)
client.on('connect', function() {
client.publish("lamp/status", status + ' ' + location, function() {
console.log("Message is published");
client.end();
resolve('Done Sending');
});
});
});
mqttPromise.then(
function(data) {
console.log('Function called succesfully', data);
this.emit(':ask', ON_RESPONSE, AFTER_RESPONSE);
}, function(err) {
console.log('An error occurred: ', err);
}
);
// Promise END
// this.emit(':ask', ON_RESPONSE, AFTER_RESPONSE);
// client.publish("lamp/status", status + ' ' + location);
} else if (status == 'off') {
this.emit(':ask', OFF_RESPONSE, AFTER_RESPONSE);
// client.publish("lamp/status", status + ' ' + location);
}
},
'DimIntent' : function () {
// to do here
},
'ChangeColorIntent' : function () {
// to do here
},
'ShceduleIntent' : function () {
// to do here
},
'AMAZON.HelpIntent': function () {
this.emit(':ask', HELP_MESSAGE, 'Wanna control something ?');
},
'AMAZON.StopIntent': function () {
this.emit(':tell', STOP_MESSAGE);
}
};
exports.handler = function (event, context, callback) {
const alexa = Alexa.handler(event, context, callback);
alexa.APP_ID = APP_ID;
alexa.registerHandlers(handlers);
alexa.execute();
}

我在Alexa Developer中使用Service Simulator测试了我的代码，得到了以下结果：结果图像

所以我检查了Lambda中的输出，得到了以下错误报告：Lamda 错误

有人能帮我吗？我对此一无所知，因为这是我的第一次试用：)

Answer 1

错误的关键似乎是日志中的这一行：

Cannot read property 'emit' of undefined

按照你的程序流程，它很可能出现在这里：

mqttPromise.then(
function(data) {
console.log('Function called succesfully', data);
// It's probably ocurring in this line below
this.emit(':ask', ON_RESPONSE, AFTER_RESPONSE);
}, function(err) {
console.log('An error occurred: ', err);
}
)

日志显示您尝试使用this，它是undefined，并且没有emit属性。这是因为this在Js中是如何工作的。您可以通过保存对此的引用来解决此问题

var that = this;
var mqttPromise = new Promise(function(resolve, reject) {
var options = {
port: '1883',
clientId: 'mqttjs_' + Math.random().toString(16).substr(2, 8),
username: 'username',
password: 'password',
};
var client  = mqtt.connect('mqtt://broker-address', options)
client.on('connect', function() {
client.publish("lamp/status", status + ' ' + location, function() {
console.log("Message is published");
client.end();
resolve('Done Sending');
});
});
});
mqttPromise.then(
function(data) {
console.log('Function called succesfully', data);
that.emit(':ask', ON_RESPONSE, AFTER_RESPONSE);
}, function(err) {
console.log('An error occurred: ', err);
}
);

我还建议阅读一点关于"这在Javascript中是如何工作的">

• MDN
• 堆栈溢出-"这是如何工作的">