<input type="password" id="passwordInput">
  <input type="checkbox" id="showPasswordCheckbox"> Показать пароль

const passwordInput = document.getElementById('passwordInput');
const showPasswordCheckbox = document.getElementById('showPasswordCheckbox');
showPasswordCheckbox.addEventListener('change', function() {
    if (showPasswordCheckbox.checked) {
        passwordInput.type = 'text';
    } else {
        passwordInput.type = 'password';}});