javascriptcustom-errorsobject-destructuring

Object spread an Error results in no message property

I'm trying to spread an Error so that I can alter the error without affecting the original error.

const error = new Error('Error test');

const freeError = {...error};
console.log(error, freeError);

But the output is an empty object {}. I'm expecting the freeError have at least a message property, but there is none.

Is this a part of JavaScript feature or is there something wrong with my code or engine?

I know a way to fix this, but it requires an extra work {...error, message: error.message}. So, yeah, all I need is a clarification so that I can be sure that I am not missing something. Thank you.

Solution

  • Object spread only copies enumerable own properties, and at least in some environments, the message is not an enumerable own property.

    In Chrome, it's a non-enumerable own property, and in Firefox, it's a property of Error.prototype:

    const error = new Error('Error test');

// Chrome logs an object (including "enumerable": false,)
console.log(Object.getOwnPropertyDescriptor(error, 'message'));

// Firefox logs an object (including "enumerable": false,)
console.log(Object.getOwnPropertyDescriptor(Object.getPrototypeOf(error), 'message'));

    It's implementation-dependent. I'd manually extract all properties you need:

    const error = new Error('Error test');
const { message, stack } = error;
const freeError = { message, stack };
console.log(freeError);