Nodejs custom error class throws "TypeError: ValidationError is not a constructor"

Question

Looking at some of the other questions on constructing classes, I can't figure out what I'm doing wrong here.

I have a custom error class called ValidationError that lives in the file validationError.js:

class ValidationError extends Error {
constructor(message, errors) {
    super(message);
    this.errors = errors;
    this.name = this.constructor.name;
    if (typeof Error.captureStackTrace === 'function') {
        Error.captureStackTrace(this, this.constructor);
    } else {
        this.stack = (new Error(message)).stack;
    }
}
}

module.exports = ValidationError;

I require this class in another file like so:

const { ValidationError } = require('./validationError');

And call it like this, which is the line that throws the error:

const validationError = new ValidationError('JSON failed validation.', result.errors);

The thrown error is, "TypeError: ValidationError is not a constructor".

I am on Node 10.6.4.

So what am I doing wrong here? Thanks for the help!

Looks fine to me. Are you using native ES6 or is there a transpilation step? — Bergi
– Bergi, Commented Feb 27, 2018 at 15:37
I'd recommend Error.captureStackTrace(this, new.target); (though actually this should happen inside the super call already) — Bergi
– Bergi, Commented Feb 27, 2018 at 15:38

Bergi · Accepted Answer · 2018-02-27 15:39:33Z

5

You're not exporting an object with a .ValidationError constructor, you're directly setting the class as the module.exports. So in your import it should be

const ValidationError = require('./validationError');

and not use destructuring syntax.

answered Feb 27, 2018 at 15:39

Bergi

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