can you add an auto slash in date2000-12-30 using javascript?

var date = document.getElementById('date');


function checkValue(str, max) {
  if (str.charAt(0) !== '0' || str == '00') {
    var num = parseInt(str);
    if (isNaN(num) || num <= 0 || num > max) num = 1;
    str = num > parseInt(max.toString().charAt(0)) &&
      num.toString().length == 1 ? '0' + num : num.toString();
  };
  return str;
};


date.addEventListener('input', function(e) {
  this.type = 'text';
  var input = this.value;
  if (/\D\/$/.test(input)) input = input.substr(0, input.length - 3);
  var values = input.split('/').map(function(v) {
    return v.replace(/\D/g, '')
  });
  if (values[1]) values[1] = checkValue(values[1], 12);
  if (values[2]) values[2] = checkValue(values[2], 31);

  var max = 4;
  var output = values.map(function(v, i) {
    if (v.length == max) {
      max = 2;
      return i < max ? v + ' / ' : v;
    };

    return v;
  });
  this.value = output.join('').substr(0, 14);
});

<input type="text" id="date">