To allow better interoperability with ES6 classes (which are forced to call the super() constructor) it is better to add the following condition to the HttpError constructor:

if (this.constructor === HttpError) {
    throw new TypeError('cannot construct abstract class')
}

This way the class can be extended with a concrete class like this:

class MyHttpError extends HttpError {
    constructor() {
        super();
        ...
    }
}

A variant using ES6 classes as base class is shown here but the same works with old school constructor functions as well.