function validate() {

    let usernameElement = document.getElementById('username');

    let emailElement = document.getElementById('email');

    let passwordElement = document.getElementById('password');

    let confirmPasswordElement = document.getElementById('confirm-password');

    let companyElement = document.getElementById('company');

    let submitElement = document.getElementById('submit');

    let companyNumberElement = document.getElementById('companyNumber');

    let companyInfoElement = document.getElementById('companyInfo');

    let validElement = document.getElementById('valid');




    let pattUsername = /^[A-Za-z0-9]{3,20}$/;

    let pattEmail = /^\w+\@[\w+\.\w+]+$/;

    let pattPassw = /^\w{5,15}$/;

    let checked = false;




    submitElement.addEventListener('click', (e) => {

        let correct = true;

        validElement.style.display = 'none';


        if (pattUsername.test(usernameElement.value) === true) {

            usernameElement.style = 'border: none';

        } else {

            usernameElement.style = 'border-color: red';

            correct = false;

        }


        if (pattEmail.test(emailElement.value) === true) {

            emailElement.style = 'border: none';

        } else {

            emailElement.style = 'border-color: red';

            correct = false;

        }


        if (pattPassw.test(passwordElement.value) === true) {

            passwordElement.style = 'border: none';

        } else {

            passwordElement.style = 'border-color: red';

            correct = false;

        }


        if (confirmPasswordElement.value === passwordElement.value) {

            confirmPasswordElement.style = 'border: none';

        } else {

            confirmPasswordElement.style = 'border-color: red';

            passwordElement.style = 'border-color: red';

            correct = false;

        }


        if (companyNumberElement.value >= 1000 && companyNumberElement.value <= 9999) {

            companyNumberElement.style = 'border: none';

        } else if (checked) {

            companyNumberElement.style = 'border-color: red';

            correct = false;

        }


        if (correct) {

            validElement.style.display = 'block';

        } else {

            validElement.style.display = 'none';

        }


        event.preventDefault();

    });


    companyElement.addEventListener('change', (e) => {

        if (e.currentTarget.checked) {

        companyInfoElement.style.display = 'block';

        } else {

        companyInfoElement.style.display = 'none';

        }

        validElement.style.display = 'none';

        checked = true;

    });

}