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AWS Lambda function global variables

I am writing an AWS Lambda function in JavaScript (Node.js) that interacts with CodeCommit through the AWS SDK.
The communication between the services works as expected, I am getting data within the CodeCommit function, but the issue I am facing appears when I want to use this data outside of the function.
I have tried two approaches:
1. Global Variable
Code:
var aws = require('aws-sdk');
var codecommit = new aws.CodeCommit({ apiVersion: '2015-04-13' });
var repoName = ''; // Declared my global variable here
exports.handler = function(event, context) {
var commitId = "69a5f8eeba340d71ba41b8f20d77cc20b301ff52"
var repository = "my-repository"
var params = {
repositoryName: repository
};
codecommit.getRepository(params, function(err, data) {
if (err) {
console.log(err);
var message = "Error getting repository metadata for repository " + repository;
console.log(message);
context.fail(message);
} else {
console.log('Repository Name:', data.repositoryMetadata.repositoryName); // Shown with data
repoName = data.repositoryMetadata.repositoryName; // Setting the variable
console.log('Account Id:', data.repositoryMetadata.accountId); // Shown with data
}
});
console.log(repoName); // Shown as blank in the output
};
Output:
The last written "console.log" is the first to print in the execution results, but shows blank. The two other console.log (within the functions) are then printed, and they show the data.
2. Function
Code:
var aws = require('aws-sdk');
var codecommit = new aws.CodeCommit({ apiVersion: '2015-04-13' });
exports.handler = function(event, context) {
var commitId = "69a5f8eeba340d71ba41b8f20d77cc20b301ff52"
var repository = "my-repository"
var repoData = getRepository(repository)
console.log('Repository Name:', repoData.repositoryName);
console.log('Account Id:', repoData.accountId);
};
function getRepository(repository) {
var params = {
repositoryName: repository
};
codecommit.getRepository(params, function(err, data) {
if (err) {
console.log(err);
var message = "Error getting repository metadata for repository " + repository;
console.log(message);
context.fail(message);
} else {
var repoData = {};
repoData.repositoryName = data.repositoryMetadata.repositoryName;
repoData.accountId = data.repositoryMetadata.accountId;
console.log(repoData); // Shows output in execution results when lines 11 & 12 are commented
return repoData;
}
});
}
Output:
{
"errorType": "TypeError",
"errorMessage": "Cannot read property 'repositoryName' of undefined",
"trace": [
"TypeError: Cannot read property 'repositoryName' of undefined",
" at Runtime.exports.handler (/var/task/index.js:57:46)",
" at Runtime.handleOnce (/var/runtime/Runtime.js:66:25)"
]
}
Conclusion
None of those approaches worked. The data is always visible within the function but never outside of it. I suspect that the code outside of the function executes before the function itself, and I wonder if I could make the code to wait that the function has been executed before doing the console.log (and other actions after it). Or maybe I am wrong on another level?

You are using a callback model, in which case the console.log in the first example is being hit before the code in the callback. A better option would be to use async/await.
var aws = require('aws-sdk');
var codecommit = new aws.CodeCommit({ apiVersion: '2015-04-13' });
var repoName = ''; // Declared my global variable here
exports.handler = async function(event, context) {
var commitId = "69a5f8eeba340d71ba41b8f20d77cc20b301ff52"
var repository = "my-repository"
var params = {
repositoryName: repository
};
var data = await codecommit.getRepository(params).promise();
console.log('Repository Name:', data.repositoryMetadata.repositoryName); // Shown with data
repoName = data.repositoryMetadata.repositoryName; // Setting the variable
console.log('Account Id:', data.repositoryMetadata.accountId); // Shown with data
console.log(repoName);
};
Notice that I'm not catching the error here, but if you wanted to you can use a try/catch block. Just be sure you throw a new error in that case if you want the function to fail.

Unable to deploy firebase function

Node.js command prompt is simply ignoring this function, while the other functions are getting deployed, I am not getting any error either.
var database = admin.database();
var postsRef = database.ref("/posts");
postsRef.on('child_added', addOrUpdateIndexRecord);
function addOrUpdateIndexRecord(dataSnapshot) {
// Get Firebase object
var firebaseObject = dataSnapshot.val();
// Specify Algolia's objectID using the Firebase object key
firebaseObject.objectID = dataSnapshot.key;
// Add or update object
index.saveObject(firebaseObject, function(err, content) {
if (err) {
throw err;
}
console.log('Firebase object indexed in Algolia', firebaseObject.objectID);
});
}

If it's a database trigger function, then the syntax you are using is not correct. Try doing this way:
exports.updateposts = functions.database.ref("posts/")
.onWrite(event => {
//Do whatever you want to do with trigger
});

(Javascript Node.js) How to get varibles from a IIFE

Please see my code below:
I am trying to assign the recordset to a variable, can use index.js to call this variable out.
I am able to console.log the recordset. But when I call this IIFE, it is always says undefined.
var mssql = require('mssql');
var dbcon = require('./dbcon');
var storage = (function () {
var connection = new mssql.Connection(dbcon);
var request = new mssql.Request(connection);
connection.connect(function (recordset) {
request.query('select getdate()', function (err, recordset) {
console.dir(recordset);
});
connection.close();
});
})();
module.exports = storage;
index.js
var storage = require('./storage');
"AMAZON.HelpIntent": function (intent, session, response) {
storage(function (recordset){
var speechOutput = 'Your result is '+recordset;
response.ask(speechOutput);
});
However, I can't get the recordset. I got "Your result is {object, object}. "

that's because the IIFE is executing right away, try returning a function instead and then executing that function when you import that module,
var storage = (function(mssql, dbcon) {
return function() {
var connection = new mssql.Connection(dbcon);
var request = new mssql.Request(connection);
connection.connect(function(recordset) {
request.query('select getdate()', function(err, recordset) {
console.dir(recordset);
});
connection.close();
});
}
})(mssql, dbcon);
and I don't understand why you need the IIFE, why don't you just assign the function to the variable?
If you're trying to assign the variable "recordset" to "storage" then this will never work as "connection.connect" is an asynchronous function, and in that case you should think about callback functions or promises.
Update
Based on your request, here's an implementation with a callback function and how it's used
var mssql = require('mssql');
var dbcon = require('./dbcon');
var storage = function(callback) {
var connection = new mssql.Connection(dbcon);
var request = new mssql.Request(connection);
connection.connect(function(recordset) {
request.query('select getdate()', function(err, recordset) {
if(!err && callback){
callback(recordset);
}
connection.close();
});
});
}
module.exports = storage;
// --------------------------------------------------
// implementation in another module
var storage = require("module_path"); // (1)
var answer;
storage(function(recordset){ // (2)
answer = recordset;
console.log(answer); // actual data, (3)
// implement your logic here
});
console.log(answer); // undefined (4)
// --------------------------------------------------
How this code works:
- You start by calling the storage method and sending it a callback method.
- The whole point of the callback function is that you won't wait for the result, your code will actually continue working at the same time that the storage method is connecting to the database and trying to get the data, ans since db operations are much slower, line(4) will execute before line(3).
- The flow of work will be as follows:
line (1)
line (2)
line (4)
line (3) at sometime in the future when the data is retrieved from database
- To see this more clearly, try doing this at the last line,
setTimeout(function(){console.log(answer);}, 3000);
This will wait for sometime until the data comes back;

exported variables got undefined while functions get exported in node js

I am creating the nodejs application which uses the mongodb.
I am connecting to mongodb only once. I want to use db in all other api's so as to achieve the connection pooling.
I have following code for mongodb connectivity:
var mongodb = require('mongodb');
var MongoClient = require('mongodb').MongoClient;
var db;
var mongoUrl = "mongodb://localhost:27017/testDB";
/**
* Connects to the MongoDB Database with the provided URL
*/
exports.connect = function(callback){
if(!db){
MongoClient.connect(mongoUrl, function(err, _db){
if (err) { throw new Error('Could not connect: '+err); }
db = _db;
console.log(db);
connected = true;
console.log(connected +" is connected?");
callback(db);
});
}else{
console.log("Not connected tis time as I am already connected");
callback(db);
}
};
exports.db = db;
I am calling connect only once when server starts from app.js. Whenever other api such as signin, register get called, they should simply use db that is exported.
So my api calls will something like(please ignore the syntax error in api call :D):
var mongo = require('./mongo');
collection = mongo.db.collection("testCollection");
// Here mongo.db id undefined
collection.findOne({"name":"John"}, function(err, result){
// Do your stuff with result here
});
From other stackoverflow posts, I tried something like in mongo.js as
module.export{
db: db,
connect : function(callback){
//function code goes here
}
}
But still I am getting the undefined for mongo.db
How would I access mongo.db in my other files?
Thanks

The reason this happens is, because connect overwrites db in the module. The exports.db=db; is not executed after calling your connect function, but on execution of the module import.
So, when you call connect, db is set to another variable, but that is not exposed outside.
Didn't do much JS lately, but this should do it:
module.exports = new mongobj();
function mongobj() {
this.db = null;
this.connect = function(callback) { /* your connect code set mongobj.db */
this.db = /* new value */ ;
}
}
When you import the module, you get the object. Accessing the objects db property will always expose the latest db value set by the connect function of the module.
var mongo = require('yourmodule');
// mongo.db is null
mongo.connect(some callback);
// mongo.db is set

This connection add in main script file...
var mongodb = require('mongodb');
var mongodb = require('mongodb');
var MongoClient = require('mongodb').MongoClient;
var mongoUrl = "mongodb://localhost:27017/testDB";
ObjectId = module.exports = require("mongojs").ObjectId;
MongoClient.connect(mongoUrl, function(err, database){
if(err){
console.log("mongodb error >>"+err);
} else {
db = module.exports = database;
}});
db.collection('game_users').findOne({_id:ObjectId("123456789")},function(err, data) {});

define an object:
var db = {__db: undefined}
and then:
exports.db = db
const db = require('./mongo').db.__db

TypeError thrown when library is included in express

I've come across a very peculiar bug that I can't seem to solve. In Node.js, I have an API wrapper library called Markitable:
var request = require('request');
var Q = require('q');
/**
* Markit on Demand API Client
* #constructor
* #author Chandler Freeman <chandler.freeman#gmail.com>
*/
var Markitable = function() {
};
module.exports = Markitable;
endpoints = {
lookup: 'http://dev.markitondemand.com/Api/v2/Lookup',
quote: 'http://dev.markitondemand.com/Api/v2/Quote',
interactivechart: 'http://dev.markitondemand.com/Api/v2/InteractiveChart'
};
/**
* Company lookup
* #httpMethod GET
* #param {ticker} String A string containing the ticker for the stock
* #param {callback} callback (Optional) If callback is passed, than the function will use callbacks
* #promises yes By default, this function uses promises
*/
Markitable.prototype.lookup = function(ticker, callback) {
var options = {
url: endpoints.lookup,
headers: this.headers,
qs: { 'input': ticker.toUpperCase() },
method: 'GET',
json: true
};
if (!callback) {
var d = Q.defer();
request(options, function(err, httpResponse, body) {
if (err) return d.reject(err);
d.resolve(body);
});
return d.promise;
}
else
request(options, callback);
};
As you can see, all it does is fetch data from the Markit on Demand API and return a Q promise. However, every time I include the
var Markitable = require('markitable');
statement anywhere in my code, when I navigate to the / route of my application I receive
Failure on / route: TypeError: Cannot read property 'user' of undefined
I am using Express I have absolutely no idea at all why this is happening; I've reread the source several times, checked source control changes, everything, yet I can't find the root of the issue. This behavior only persists when the library is included; as soon as I remove that statement, everything works perfectly. I don't understand because the code for this library was the exact same code I used from another library I wrote, and the first one looks great. Here is the code for my routes file:
var User = require('../app/models/user');
var Robinhood = require('marian');
var util = require('util');
var Q = require('q');
module.exports = function(app, passport) {
// =========================================
// Table of Contents(Search by name)
//
// 1. Root
//
// =========================================
// ********************* 1. Root *********************
app.get('/', isLoggedIn, asyncCallback(function*(req, res) {
rh = new Robinhood(req.user.local.rhtoken);
var viewData = { user : req.user };
try {
// e: <Cannot read property user of undefined>
viewData.rhUser = yield rh.getUser();
viewData.rhUser.basic_info = yield rh.getBasicInfo();
viewData.rhPortfolio = yield rh.getPortfolio();
viewData.getOrders = yield rh.getOrders();
viewData.rhAccount = yield rh.getAccount();
viewData.active = { page : 'dashboard' };
res.render('main_pages/maindashboard.ejs', viewData);
}
catch(e) {
console.log("Failure on / route: " + e);
res.render('meta/500.ejs');
}
}));
};
function isLoggedIn(req, res, next) {
if (req.isAuthenticated())
return next();
res.redirect('/login');
}
// Code originally from James Long
// http://jlongster.com/A-Study-on-Solving-Callbacks-with-JavaScript-Generators
function asyncCallback(gen) {
return function() {
return Q.async(gen).apply(null, arguments).done();
};
}
Any ideas about why this strange behavior may be occurring? I can't imagine why importing a library would affect the 'req' object, but somehow it does. Could this be a bug in Express?
EDIT:
Forgot the stack trace:
TypeError: Cannot read property 'user' of undefined
at Robinhood.getUser (/vagrant/StockFire/node_modules/marian/index.js:110:26)
at /vagrant/StockFire/app/routes.js:28:40
at next (native)
at Function.continuer (/vagrant/StockFire/node_modules/q/q.js:1278:45)
at /vagrant/StockFire/node_modules/q/q.js:1305:16
at /vagrant/StockFire/app/routes.js:226:29
at Layer.handle [as handle_request] (/vagrant/StockFire/node_modules/express/lib/router/layer.js:95:5)
at next (/vagrant/StockFire/node_modules/express/lib/router/route.js:131:13)
at isLoggedIn (/vagrant/StockFire/app/routes.js:217:16)
at Layer.handle [as handle_request] (/vagrant/StockFire/node_modules/express/lib/router/layer.js:95:5)
at next (/vagrant/StockFire/node_modules/express/lib/router/route.js:131:13)
at Route.dispatch (/vagrant/StockFire/node_modules/express/lib/router/route.js:112:3)
at Layer.handle [as handle_request] (/vagrant/StockFire/node_modules/express/lib/router/layer.js:95:5)
at /vagrant/StockFire/node_modules/express/lib/router/index.js:277:22
at Function.process_params (/vagrant/StockFire/node_modules/express/lib/router/index.js:330:12)
at next (/vagrant/StockFire/node_modules/express/lib/router/index.js:271:10)

Solved the issue. Simple bug, but very hard to find. I discovered that a variable named endpoints existed in both libraries, but neither was declared with var, meaning that the variable was overwritten since they both existed in the javascript global scope. Lessons learned: Always check variable scope.