donate.js

//  form display script 

    var personalForm = document.querySelector('#personal-info'),
        medicalForm = document.querySelector('#medical-info'),
        medicalBlock = document.querySelector('.medical-info');

    personalForm.addEventListener('submit', (e) => {
        e.preventDefault();
        medicalBlock.style.display = "block";
    })

    // Date Validator  
  
      var dob = document.querySelector('#dob');
      dob.addEventListener('change', checkAge);

      function checkAge(e) {
          console.log(dob.value);
          var date = dob.value.split('-'),
              year = date[0],
              month = date[1],
              day = date[2],
              today = new Date();

          var age = today.getFullYear() - year;
          var m = today.getMonth() - month;
          if (m < 0 || (m === 0 && today.getDate() < Date(dob.value))) {
              age--;
          }
          if (age < 18) {
              alert('You are not eligible to donate blood');
              dob.value = '';
          }
      }