expressjs not throwing error on Parse queries (parse-server) - express

Question

I have a parse-server setup on expressjs like here.
But sometimes it's not showing errors inside Parse functions. Example:
// Parse Server is setup
// Parse Server plays nicely with the rest of your web routes
app.get('/', function(req, res) {
var pageQuery = new Parse.Query('Page');
pageQuery.get('id').then(function(page) {
someObject.undefinedProp = false;
res.send(page);
}, function(error) {
res.send(error);
});
});
No errors displayed, but with this code:
// Parse Server is setup
// Parse Server plays nicely with the rest of your web routes
app.get('/', function(req, res) {
someObject.undefinedProp = false;
res.send('ok');
});
I have this error displayed:
ReferenceError: someObject is not defined
(For this example I have the exact same configuration as the Parse Server Example)
I just want to have the errors displayed inside my Parse functions.
Any ideas?
Thank you for your help!

Answer 1

Your issue is actually an issue caused by Promises.
When you call pageQuery.get('id'), the get method returns a Promise instance. The then method of the Promise is how you set up your callback that will fire on the successful completion of the get operation.
In order to get a reference to the error that should occur when you attempt to reference someObject.undefinedProp, you'll also need to set up an error handler on that Promise object by calling its catch method.
app.get('/', function(req, res) {
var pageQuery = new Parse.Query('Page');
pageQuery.get('id').then(function(page) {
someObject.undefinedProp = false;
// the error thrown here will be caught by the Promise object
// and will only be available to the catch callback below
res.send(page);
}, function(error) {
// this second callback passed to the then method will only
// catch errors thrown by the pageQuery.get method, not errors
// generated by the preceding callback
res.send(error);
}).catch(function (err) {
// the err in this scope will be your ReferenceError
doSomething(err);
});
});
Here, check out the following article and scroll down to the section heading "Advanced mistake #2: catch() isn't exactly like then(null, ...)".
https://pouchdb.com/2015/05/18/we-have-a-problem-with-promises.html