CODEWITHSUNDEEP
javascriptjsonnode.jsexpress
Jon
Jon

Reputation: 83

How to create Node.js custom errors and have the stack property return after res.json()

I’m attempting to create custom error objects in Node that use Error as the prototype and then to return these errors to the client via the express res.json() method. I can create an instance of a custom error, set it’s properties but when I call res.json(), the stack property is missing. I believe this is due to JSON.stringify() not following prototypes?

I can’t see a way of creating custom error objects with an arbitrary number of properties and then use JSON.stringify() on these objects to return all the properties and the base class / superclass Error stack property. Please help! An example is below:

(function (customErrorController) {


    function CustomError() {

        this.name = 'CustomError'; // String
        this.message = null; // String
        this.errorCode = null; // String
        // this.stack exists as CustomError inherits from Error
    }

    CustomError.prototype = new Error();


    customErrorController.init = function (app) {

        app.get('/test', function (req, res) {

            var customError = new CustomError();
            customError.message = 'The Message';
            customError.errorCode = 'Err001';

            console.log(customError.stack); // This logs the stack fine

            res.json(customError); // The stack is missing when outputting the object as JSON

        });
    };

})(module.exports);

Upvotes: 1

Views: 3838

Answers (1)

Jon
Jon

Reputation: 83

Thanks for the comments. From these and from a bit more digging, I’m now using the following code to create custom errors and have the correct stack on the stack property return after calling res.json() with the error:

// Redefine properties on Error to be enumerable
Object.defineProperty(Error.prototype, 'message', { configurable: true, enumerable: true });
Object.defineProperty(Error.prototype, 'stack', { configurable: true, enumerable: true });


(function (customErrorController) {

    function CustomError(message, errorCode) {

        Error.captureStackTrace(this, CustomError);

        this.name = 'CustomError'; // String
        this.message = message; // String
        this.errorCode = errorCode; // String
    }

    CustomError.prototype = Object.create(Error.prototype);

    customErrorController.init = function (app) {

        app.get('/test', function (req, res) {

            var customError = new CustomError('The Message', 'Err001');
            res.json(customError); // The stack property is now included

        });
    };

})(module.exports);

Upvotes: 1

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