How to simplify this code - node.js

Question

Here I am trying to create a new train and adding seat available information for next 5 days to that train. Here I am doing things repetitively. I wanted to know how to simplify this code.
here I have used express, mongoose and moment.js to generate date.
app.post("/admin",[
hasAccess('admin'),
function(req,res,next){
var today = moment();
Train.create(req.body.train,function(err,train){
if(err){
console.log(err);
}else{
Availability.create({date:moment(today).add(0, 'days').format("DD-MM-YYYY"),available:10},function(err,avail){
if(err){
console.log(err);
}else{
train.availabilities.push(avail);
Availability.create({date:moment(today).add(1, 'days').format("DD-MM-YYYY"),available:10},function(err,avail){
if(err){
console.log(err);
}else{
train.availabilities.push(avail);
Availability.create({date:moment(today).add(2, 'days').format("DD-MM-YYYY"),available:10},function(err,avail){
if(err){
console.log(err);
}else{
train.availabilities.push(avail);
Availability.create({date:moment(today).add(3, 'days').format("DD-MM-YYYY"),available:10},function(err,avail){
if(err){
console.log(err);
}else{
train.availabilities.push(avail);
Availability.create({date:moment(today).add(4, 'days').format("DD-MM-YYYY"),available:10},function(err,avail){
if(err){
console.log(err);
}else{
train.availabilities.push(avail);
train.save();
res.redirect("/trains/"+train._id);
}
})
}
})
}
})
}
})
}
})
}
});
}
]);

Answer 1

1 - Using promises
app.post("/admin", [
hasAccess('admin'),
function (req, res, next) {
var today = moment();
const days = [0, 1, 2, 3, 4];
let createdTrain;
Train.create(req.body.train)
.then(train => {
createdTrain = train;
return Promise.all(days.map(day => {
return Availability.create({
date: moment(today).add(day, 'days').format("DD-MM-YYYY"),
available: 10
});
}));
})
.then(result => {
createdTrain.availabilities = result;
createdTrain.save();
})
.then(saved => {
res.redirect("/trains/" + saved._id);
})
.catch(err => {
console.log(err);
});
}
]);
2 - Using async await [node 7.6 +]
app.post("/admin", [
hasAccess("admin"),
async (req, res, next) => {
try {
const today = moment();
const DAYS = [0, 1, 2, 3, 4];
const train = await Train.create(req.body.train);
const result = await Promise.all(
DAYS.map(day => {
return Availability.create({
date: moment(today)
.add(day, "days")
.format("DD-MM-YYYY"),
available: 10
});
})
);
train.availabilities = result;
const saved = await train.save();
res.redirect("/trains/" + saved._id);
} catch (err) {
console.log(err);
}
}
]);

Answer 2

You can also use async package for creating availability object in parallel by using async.parallel, this make your execution fast and create one function that can create availability object.
app.post("/admin", [
hasAccess('admin'),
function (req, res, next) {
var today = moment();
Train.create(req.body.train, function (err, train) {
if (err) {
console.log(err);
} else {
var functionArr = [];
for (var i = 0; i < 5; i++) {
var availFunction = function (i, callback) {
availability(moment(today), 0, 10, function (err, avail) {
if (err) {
return callback(err);
}
return callback(null, avail);
});
}
functionArr.push(availFunction);
}
async.parallel([
functionArr
], function (err, results) {
if (err) {
console.log(err);
}
train.availabilities.push(results);
train.save();
res.redirect("/trains/" + train._id);
});
}
});
}
]);
function availability(date, days, seats, callback) {
Availability.create({
date: moment(date).add(days, 'days').format("DD-MM-YYYY"),
available: seats
}, function (err, avail) {
if (err) {
return callback(err);
} else {
return callback(null, avail);
}
});
}