JSFiddle - React, Tailwind, and code Playground

JavaScript

function validateInput(data, additionalValid) {
    let { errors } = additionalValid(data);
    const { login, email } = data;

    return Promise.all([
        User.findOne({ login }, (err, user) => {
            if (err) return err;
            if (user) {
                if (user.login === login) {
                    console.log(user.login);
                    errors.login = 'There is user with such username';
                }
            }
        }),
        User.findOne({ email }, (err, user) => {
            if (err) return err;
            if (user) {
                if (user.email === email) {
                    console.log(user.email);
                    errors.email = 'There is user with such email';
                }
            }
        })
    ]).then(() => {
        return {
            errors,
            isValid: Object.keys(errors).length === 0
        };
    });
}