Node.js "callback not defined" when trying to to a http request - node.js

Question

totally new to Node.js and this callback thing is driving me nuts.
I am writing a Skill for an Amazon Echo. As part of this I am trying to send an SMS using BulkSMS.com via a HTTP Request. The http.request has a callback which parses the response. (To take the BulkSMS API out of the equation in the example below I am just trying to get it working using a http request to Random.org (i.e. www.random.org/integers/?num=1&min=1&max=10&col=1&base=10&format=plain&rnd=new)
However I am getting an error saying that the callback is not defined.
{
"errorMessage": "callback is not defined",
"errorType": "ReferenceError",
"stackTrace": [
"Emergency.eventHandlers.onLaunch (/var/task/index.js:54:11)",
"AlexaSkill.requestHandlers.LaunchRequest (/var/task/AlexaSkill.js:16:37)",
"AlexaSkill.execute (/var/task/AlexaSkill.js:97:24)",
"exports.handler (/var/task/index.js:100:15)"
]
}
I am sure I am doing something totally stupid and for that I apologize, but I just can't see it.
Here is the onLaunch event handler in my index.js. Any help greatly appreciated.
Emergency.prototype.eventHandlers.onLaunch = function (launchRequest, session, response) {
console.log("Emergency onLaunch requestId: " + launchRequest.requestId + ", sessionId: " + session.sessionId);
console.log("Attempting to send SMS");
callback = function(response) {
var str = '';
console.log("In callback");
//another chunk of data has been recieved, so append it to `str`
response.on('data', function (chunk) {
str += chunk;
console.log("Getting Data");
});
//the whole response has been recieved, so we just print it out here
response.on('end', function () {
console.log("End of response");
console.log(str);
});
}
http.request(options, callback).end();
console.log("Finished sending SMS");
var speechOutput = "<speak>SMS sent</speak>";
response.tell(speechOutput);
};
Full index.js is below.
'use strict';
/**
* App ID for the skill
*/
var APP_ID = "amzn1.ask.skill.eb8cf94a-848f-45ae-9792-xxxxxxxxxx";
/**
* The AlexaSkill prototype and helper functions
*/
var AlexaSkill = require('AlexaSkill');
var http = require('http');
var request = require("request");
//var Alexa = require('alexa-sdk');
var SKILL_NAME = 'Emergency';
var Emergency = function () {
AlexaSkill.call(this, APP_ID);
console.log("APP_ID set");
};
var alexaResponse = "";
//The url we want is: 'www.random.org/integers/? num=1&min=1&max=10&col=1&base=10&format=plain&rnd=new'
var options = {
host: 'www.random.org',
path: '/integers/?num=1&min=1&max=10&col=1&base=10&format=plain&rnd=new'
};
// Extend AlexaSkill
Emergency.prototype = Object.create(AlexaSkill.prototype);
Emergency.prototype.constructor = Emergency;
Emergency.prototype.eventHandlers.onSessionStarted = function (sessionStartedRequest, session) {
console.log("Emergency onSessionStarted requestId: " + sessionStartedRequest.requestId
+ ", sessionId: " + session.sessionId);
// any initialization logic goes here
};
Emergency.prototype.eventHandlers.onLaunch = function (launchRequest, session, response) {
console.log("Emergency onLaunch requestId: " + launchRequest.requestId + ", sessionId: " + session.sessionId);
console.log("Attempting to send SMS");
callback = function(response) {
var str = '';
console.log("In callback");
//another chunk of data has been recieved, so append it to `str`
response.on('data', function (chunk) {
str += chunk;
console.log("Getting Data");
});
//the whole response has been recieved, so we just print it out here
response.on('end', function () {
console.log("End of response");
console.log(str);
});
}
http.request(options, callback).end();
console.log("Finished sending SMS");
var speechOutput = "<speak>SMS sent</speak>";
response.tell(speechOutput);
};
Emergency.prototype.eventHandlers.onSessionEnded = function (sessionEndedRequest, session) {
console.log("Emergency onSessionEnded requestId: " + sessionEndedRequest.requestId
+ ", sessionId: " + session.sessionId);
// any cleanup logic goes here
};
Emergency.prototype.intentHandlers = {
// register custom intent handlers
EmergencyIntent: function (intent, session, response) {
// Get a random "never" phrase from the list
}
};
// Create the handler that responds to the Alexa Request.
exports.handler = function (event, context) {
// Create an instance of the Emergency skill.
var emergency = new Emergency();
emergency.execute(event, context);
};

Answer 1

However I am getting an error saying that the callback is not defined.
That's because of 'use strict'; mode.
First, strict mode makes it impossible to accidentally create global variables. In normal JavaScript mistyping a variable in an assignment creates a new property on the global object and continues to "work" (although future failure is possible: likely, in modern JavaScript). Assignments which would accidentally create global variables instead throw in strict mode:
More on this in MDN
accidentalGlobalVariable = 'hello world';
console.log(accidentalGlobalVariable); // logs hello world
In strict mode,
'use strict';
accidentalGlobalVariable = 'hello world';
console.log(accidentalGlobalVariable); // errors out
Error
accidentalGlobalVariable = 'hello world';
^
ReferenceError: accidentalGlobalVariable is not defined
In your code sample, If I run without strict mode it works,
var http = require('http');
var options = {
host: 'www.random.org',
path: '/integers/?num=1&min=1&max=10&col=1&base=10&format=plain&rnd=new'
};
callback = function (response) {
console.log('response statusCode', response.statusCode);
};
http.request(options, callback).end();
but if I run with strict mode,
'use strict';
var http = require('http');
var options = {
host: 'www.random.org',
path: '/integers/?num=1&min=1&max=10&col=1&base=10&format=plain&rnd=new'
};
callback = function (response) {
console.log('response statusCode', response.statusCode);
};
http.request(options, callback).end();
I too get error because strict mode errors out callback
callback = function (response) {
^
ReferenceError: callback is not defined
you can remedy it by
Using var or let in assignment.
var callback = function (response) {
console.log('response statusCode', response.statusCode);
};
Eliminating the need of callback all together and use an anonymous function instead.
http.request(options, function (response) {
console.log('response statusCode', response.statusCode);
}).end();