UnhandledPromiseRejectionWarning, Express.js and Node.js - html

Question

I am completely new to Node.js and Express.js and have been trying to work through some examples to integrate the Shippo API into my E-commerce web app but I'm getting some errors that I just can't solve despite reviewing my code several times.
I get the UnhandledPromiseRejectionWarning error, which, from I've read online, means that somewhere in my code there is something a .then() section which does not include a "catch" or a "what to-do" is the request returns an error. Any help would be greatly appreciated.
This is my code:
var express = require('express')
var app = express()
var http = require('http');
var Raven = require('raven');
var shippo = require('shippo')('ACCESS_TOKEN');
var engines = require('consolidate');
const bodyParser = require('body-parser');
const path = require('path');
app.use(bodyParser.urlencoded({extended: true}));
app.use(bodyParser.json());
app.engine('html', engines.mustache);
app.set('view engine', 'html');
//app.use(express.static(path.join(_dirname,'/')));
app.get('/', function (req, res) {
res.render('Index.html');
})
app.post('/', function (req, res) {
var addressFrom = {
"object_purpose":"PURCHASE",
"name": "SENDER_NAME",
"company":"Shippo",
"street1":"215 Clayton St.",
"city":"San Francisco",
"state":"CA",
"zip":"94117",
"country":"US", //iso2 country code
"phone":"[phone]",
"email":"SENDER_EMAIL",
};
// example address_to object dict
var addressTo = {
"object_purpose":"PURCHASE",
"name": req.body.fnames + ' ' + req.body.lnames,
"company": req.body.company,
"street1":req.body.street,
"city":req.body.city,
"state":req.body.state,
"zip":req.body.zipcode,
"country": req.body.country, //iso2 country code
"phone":"[phone]",
"email":"support#goshippo.com",
};
// parcel object dict
var parcelOne = {
"length":"5",
"width":"5",
"height":"5",
"distance_unit":"in",
"weight":"2",
"mass_unit":"lb"
};
var shipment = {
"object_purpose": "PURCHASE",
"address_from": addressFrom,
"address_to": addressTo,
"parcels": [parcelOne],
"submission_type": "DROPOFF"
};
shippo.transaction.create({
"shipment": shipment,
"servicelevel_token": "ups_standard",
"carrier_account": 'CARRIER_TOKEN',
"label_file_type": "PDF"
})
.then(function(transaction) {
shippo.transaction.list({
"rate": transaction.rate
})
.then(function(mpsTransactions) {
mpsTransactions.results.forEach(function(mpsTransaction){
if(mpsTransaction.object_status == "SUCCESS") {
console.log("Label URL: %s", mpsTransaction.label_url);
console.log("Tracking Number: %s", mpsTransaction.tracking_number);
console.log("E-Mail: %s", mpsTransaction.object_owner);
console.log(mpsTransaction.object_status);
res.status(200).send("Label can be found under: " + mpsTransaction.label_url);
} else {
// hanlde error transactions
console.log("Message: %s", mpsTransactions.messages);
}
});
})
}, function(err) {
// Deal with an error
console.log("There was an error creating transaction : %s", err.detail);
res.send("something happened :O")
});
})
app.post('/successp', function (req, res) {
var token = req.body.stripeToken; // Using Express
// Charge the user's card:
var charge = stripe.charges.create({
amount: 1000,
currency: "eur",
description: "Example charge",
source: token,
}, function(err, charge) {
// asynchronously called
});
res.send('Thanks!')
})
app.post('/successp', function (req, res) {
var token = req.body.stripeToken; // Using Express
// Charge the user's card:
var charge = stripe.charges.create({
amount: 1000,
currency: "eur",
description: "Example charge",
source: token,
}, function(err, charge) {
// asynchronously called
});
res.send('Thanks!')
})
app.listen(3000, function () {
console.log('Example app listening on port 3000!')
})
And this is the Error I get:
Example app listening on port 3000!
(node:2378) UnhandledPromiseRejectionWarning
(node:2378) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:2378) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
I'm also not completely sure about the purpose for some of the lines (again, i'm very new to express and node.js). What is engine and mustache? also, I see that this sample code uses APP.POST('/succesp', function(req, res)...), what exactly is that '/succesp'? Another html file I need to create? Also, what is that "app.use(express.statc([ath.join(_dirnam,'/')));" at the beginning?

Answer 1

You need to be a little careful using the format then(FN, errorFn), because if there's an error inside the then, the errorFn won't catch it. It's better to use then(fn).catch(errorFn). This will allow all errors in any then above to filter down to the last catch for handling.
For example, the first call properly catches the error, the second doesn't:
function fn() {
return Promise.resolve("good")
}
fn()
.then(r => {
throw ("whoops")
})
.catch(err => console.log(err)) //<-- catch works here
fn()
.then(r => {
throw ("whoops")
},
err => console.log(err) // this can't catch the error above; it will only catch rejections on fn()
)
It doesn't show in the snippet but if you look at the console, you'll see an unhandled rejection error.
In your code, you can flatten out the promise chain by returning the promise from shippo.transaction.list. Then you can add a catch at the end to handle errors.
shippo.transaction.create({
"shipment": shipment,
"servicelevel_token": "ups_standard",
"carrier_account": 'CARRIER_TOKEN',
"label_file_type": "PDF"
})
.then(function(transaction) {
return shippo.transaction.list({ // return this promise
"rate": transaction.rate
})
.then(function(mpsTransactions) { // so this can flatten out
mpsTransactions.results.forEach(function(mpsTransaction){
if(mpsTransaction.object_status == "SUCCESS") {
console.log("Label URL: %s", mpsTransaction.label_url);
console.log("Tracking Number: %s", mpsTransaction.tracking_number);
console.log("E-Mail: %s", mpsTransaction.object_owner);
console.log(mpsTransaction.object_status);
res.status(200).send("Label can be found under: " + mpsTransaction.label_url);
} else {
// hanlde error transactions
console.log("Message: %s", mpsTransactions.messages);
}
});
})
.catch(function(err) { // catch errors
// Deal with an error
console.log("There was an error creating transaction : %s", err.detail);
res.send("something happened :O")
});
})
Since this is hard to run locally without all the pieces, I'm not positive about the source of the error, but it looks like you are sending res.status(200).send() inside a loop, which might lead to an error if it gets called twice.

Answer 2

Without reading the full code, you shouldn't try to catch an error with a callback function when using Promises. You catch errors in Promises using a .catch block
And you should also return the first promise, so that it passes to the next .then function (if your intention is to return the shippo.transaction.list as mpsTransactions)
Something like this:
shippo.transaction.create({
"shipment": shipment,
"servicelevel_token": "ups_standard",
"carrier_account": 'CARRIER_TOKEN',
"label_file_type": "PDF"
})
.then(function(transaction) {
return shippo.transaction.list({
"rate": transaction.rate
})
})
.then(function(mpsTransactions) {
mpsTransactions.results.forEach(function(mpsTransaction){
if(mpsTransaction.object_status == "SUCCESS") {
console.log("Label URL: %s", mpsTransaction.label_url);
console.log("Tracking Number: %s", mpsTransaction.tracking_number);
console.log("E-Mail: %s", mpsTransaction.object_owner);
console.log(mpsTransaction.object_status);
res.status(200).send("Label can be found under: " + mpsTransaction.label_url);
} else {
// hanlde error transactions
console.log("Message: %s", mpsTransactions.messages);
}
});
})
.catch(function (error) {
// Deal with an error
console.log("There was an error creating transaction : %s", err.detail);
res.send("something happened :O")
});