Exception handling swallows errors about dexie.js HOT 4 CLOSED

If you catch() the promise that is returned from then(), the error will be picked up as expected:

var db = new Dexie("testdb");
db.version(1).stores({ table1: "id" });
db.on('error', function(err) { console.log(err); });
db.open().then(function () {
    console.log("before");
    throw "FOO";
    console.log("after");
}).catch(function (err) {
   console.log("explicitely catched: " + err);
});

Output:

before
explicitely catched: FOO

However, db.on('error') should pick up all errors that the user code failed to explicitely catch and you have found a case where this fallback event doesnt work as expected. I have already put it in a unit test so that we wont forget to fix it.

from dexie.js.

Having debugged what happens I find that the reason db.on('error') didnt fire, was that the exception wasn't thrown in a database operation nor in a database transaction. That's why it doesnt bubble to db.on('error').

In fact, the code exception occurs when there is no ongoing transaction and the database has been successfully opened and code execution is handed over to the application code. So no db.on('error') should actually be fired.

One could argue that it would be handy with a static event on Promise (Promise.on('uncatched')) but that is another feature.

db.on('error') will only fire in the following scenarios:

• You are in a transaction scope and an exception occur and you dont catch the Promise returned from the db.transaction() method.
• You are doing a database operation that fails with an exception and you don't catch the resulting promise.

But not if:

• You are outside of a transaction and the error doesnt occur from within a database operation.

from dexie.js.

I've updated the documentation for Dexie.on.error to clarify it's behavior.

from dexie.js.

Thanks for the quick reply and explanation, I wasn't aware the default behaviour for promises is to swallow exceptions. Gah. I suppose we'll have to append .catch() to all promises then, until something better turns up.

from dexie.js.