Issue with UnhandledPromiseRejectionWarning in Mongoose/Typescript even with catch block

Question

Issue with UnhandledPromiseRejectionWarning in Mongoose/Typescript even with catch block

I'm facing an issue with an UnhandledPromiseRejectionWarning in my code. The specific scenario involves a Mongoose Index named 'id', where I am testing the insertion of a duplicate ID that should be handled appropriately.

router.post('/create/:id', jsonParser, (req: Request, res: Response) => {
    let { id } = req.params;
    if (!req.body) {
        return res.sendStatus(400)
    }

    // @TODO add validation on JSON
    let promise = Requirement.create({id: id, data: req.body.data, deleted: false});

    promise.then((requirement) => {
        return res.json(requirement);
    });

    promise.catch((reason) => {
        let err = {'error': reason};
        return res.json(err);
    });
});

The response JSON confirms that my rejection handler is being executed:

{
    "error": {
        "name": "MongoError",
        "message": "E11000 duplicate key error collection: rex.requirements index: id_1 dup key: { : \"REQ001\" }",
        "driver": true,
        "index": 0,
        "code": 11000,
        "errmsg": "E11000 duplicate key error collection: rex.requirements index: id_1 dup key: { : \"REQ001\" }"
    }
}

The warnings I am encountering are as follows:

(node:11408) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): MongoError: E11000 duplicate key error collection: rex.requirements index: id_1 dup key: { : "REQ001" }
(node:11408) [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.

javascript typescript promise

Answer 1

Answer №1

It seems like you're on the right track

var a = promise.then(…);
var b = promise.catch(…);

by creating a branch in the chain. When promise is rejected, the catch callback will handle it and fulfill promise b, however, promise a gets rejected as well without any handling.

To address this issue, consider utilizing both arguments of the then method like so:

Requirement.create({id: id, data: req.body.data, deleted: false})
.then(requirement => {
    res.json(requirement);
}, reason => {
    let err = {'error': reason};
    res.json(err);
});

Answer 2

It seems like you're on the right track

var a = promise.then(…);
var b = promise.catch(…);

by creating a branch in the chain. When promise is rejected, the catch callback will handle it and fulfill promise b, however, promise a gets rejected as well without any handling.

To address this issue, consider utilizing both arguments of the then method like so:

Requirement.create({id: id, data: req.body.data, deleted: false})
.then(requirement => {
    res.json(requirement);
}, reason => {
    let err = {'error': reason};
    res.json(err);
});

Answer 3

Answer №2

catch is used to capture errors thrown by promise, but does not catch errors from promise.then(...). If an error occurs within then, it will result in an unhandled rejection. Even if the error is not explicitly thrown, but is propagated from promise, it will still be considered uncaught within this promise.

A better approach would be:

promise
.then((requirement) => {
    return res.json(requirement);
})
.catch((reason) => {
    let err = {'error': reason};
    return res.json(err);
});

Answer 4

catch is used to capture errors thrown by promise, but does not catch errors from promise.then(...). If an error occurs within then, it will result in an unhandled rejection. Even if the error is not explicitly thrown, but is propagated from promise, it will still be considered uncaught within this promise.

A better approach would be:

promise
.then((requirement) => {
    return res.json(requirement);
})
.catch((reason) => {
    let err = {'error': reason};
    return res.json(err);
});

Issue with UnhandledPromiseRejectionWarning in Mongoose/Typescript even with catch block

Answer №1

Answer №2

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