async.parallel not executing last cllback function when using with lambda functions - node.js

Question

I am writing a lambda function in node js. I have main js file (index.js) which based on input event calls a methods in 2nd js file (loader.ls).
The issue is that after the method execution completes in loader.js, the callback in index.js is not getting executed. Below is the code
Code in index.js
var yates = require("./yatesLoader");
module.exports.handler = function(event, context) {
if(event.app === undefined || event.data === undefined){
context.fail("invalid request");
}
if(event.app === 'YatesDataLoader'){
var result = yates.sendNotification(event.data, function(err, resp){
if(err){
console.log("Error : " + JSON.stringify(err));
context.done(null, "error occured");
}
console.log("response : " + JSON.stringify(resp));
context.done(null, resp); // SUCCESS with message
});
}
};
Code in loader.js
var config = require("./config");
var optDynamo = config.DynamoDb;
var optSlack = config.Slack;
var async = require("async");
var req = require("request");
var AWS = require("aws-sdk");
AWS.config.update({
region: optDynamo.region
});
var DynamoDb = new AWS.DynamoDB();
var sendNotification = function(data, callback){
async.parallel([
sendSlackNotification.bind(null, data, cb),
saveDataToDynamoDb.bind(null, data, cb)
], function(err, results){
if (err) {
console.error("Error JSON:", JSON.stringify(err, null, 2));
return callback(err, null);
} else {
console.log("Success:", JSON.stringify(results, null, 2));
return callback(null, results);
}
});
};
var cb = function(err, resp){
if(err){
console.log("Error");
}else {
console.log("success");
}
};
var saveDataToDynamoDb = function(data, cb){
var params = {
"TableName" : optDynamo.table,
"Item" : {
"TimeStamp" : {"S" : new Date().toString() },
"ErrorMessage" : {"S" : data }
}
};
console.log("adding new data to DynamoDb");
DynamoDb.putItem(params, function(err, data){
if (err) {
console.error("Unable to add item. Error JSON:", JSON.stringify(err, null, 2));
return cb(err, null);
} else {
console.log("Added item:", JSON.stringify(data, null, 2));
return cb(null, data);
}
});
};
var sendSlackNotification = function(data, cb){
var options = {
method : 'post',
body : {"text" : data},
json : true,
url : optSlack.url
};
console.log("sending msg to slack");
req(options, function(err, resp){
if(err){
console.error("Unable to send message to Slack. Error JSON:", JSON.stringify(err, null, 2));
return cb(err, null);
} else {
console.log("Message sent to Slack:", JSON.stringify(resp, null, 2));
return cb(null, resp);
}
})
};
module.exports = {sendNotification : sendNotification};
Can someone help in understanding what is wrong here.

Answer 1

Its because of the way you are using .bind(). It is changing the arguments that get passed in to saveDataToDynamoDb() and sendSlackNotification(). So what they see is actually:
var saveDataToDynamoDb = function(data, cb, next) { ....
where next is the callback that the async library is expecting you to call. So you could call next after cb.
var saveDataToDynamoDb = function(data, cb, next){
...
DynamoDb.putItem(params, function(err, data){
if (err) {
cb(err, null);
return next(err, null);
} else {
cb(err, null);
return next(null, data);
}
});
};