Javascript object property isn't displayed but can be accessed-CodePudding

i'm creating a custom express middleware to handle errors thrown by mongoose. the error has a message property:

//works as intended
console.log(error.message); //E11000 duplicate key error collection

but when i want to send the entire object, the message property doesn't show up:

res.status(400).json(error);
/*
recieved response:
{
    "index": 0,
    "code": 11000,
    "keyPattern": {
        "name": 1
    },
    "keyValue": {
        "name": "Some Name"
    }
}
*/

destructuring doesn't work either:

res.status(400).json({ ...error });
//same response as before

it doesn't show it in Object.keys() either:

console.log(Object.keys(error)); //[ 'index', 'code', 'keyPattern', 'keyValue' ]

but this statement is true:

console.log("message" in error); //true

i don't know why it behaves this way but what is the workaround ?

CodePudding user response：

Seems like the message property on error object is non-enumerable. If a property is non-enumerable, it cannot be serialised (res.json serialises the input JSON), won't appear in Object.keys or get destructured.

Your best bet is either to explicitly set the enumerable as true on error.message, or copy the error.message on some other key inside error object.

// For initialisation 
Object.defineProperty(error, 'message', {enumerable: true, value: ''});

//OR 
const errorMessage = error.message;
error.customMessage = errorMessage;
// Now use error.customMessage instead of error.message 

// OR
// Create a new object with the above retrieved error.message

const customError = {...error, message: customMessage};
// use customError object now
res.status(400).json(customError);

More details : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty

CodePudding user response：

you should use :

let message = `${Object.values(error.keyValue)} is duplicated/already exists, please choose another one` 
console.log(message) // name is duplicated/already exists, please choose another one