Helper function to show mongoose validation errors as bad request (409) on express

mongooseValidator.js

function mongooseValidator(err, req, res, next) => {

    if (err !== 'undefined' && err.name !== 'undefined' && err.name === 'ValidationError')
        return handleValidationError(err, res);

    if (err !== 'undefined' && err.code === 11000)
        return handleDuplicateValidationError(err, res);

    next(err);
}

function handleDuplicateValidationError(err, res) {
    res.sendStatus(409);
}

function handleValidationError(err, res) {

    var errorMessage = {
        message: err.message,
        errors: []
    };

    for (var prop in err.errors) {

        errorMessage.errors.push({
            propertyName: prop,
            propertyPath: err.errors[prop].path,
            validation: err.errors[prop].kind,
            message: err.errors[prop].message || err.errors[prop].kind
        });
    }

    res.status(400).json(errorMessage);

}