Random Birthday Input

<h1>Enter your birthday</h1>

<label for="random_birthday">Birthday: </label>
<div id="random_birthday" name="random_birthday">01 June 1900</div>

<p>Is this your birthday?</p>
<button onclick="yipee()">Yes</button>
<button onclick="randomNewBirthday()">No</button>

<p id="res"></p>

<script>
  const box = document.getElementById('random_birthday');
  const res = document.getElementById('res');

  const startDate = new Date(1900, 0, 1);
  const endDate = new Date();

  let birthday;

  function randomDateGen(start, end) {
    const random_time_stamp = +start + Math.random() * (end - start);
    return [
      new Date(random_time_stamp).getDate(), 
      new Date(random_time_stamp).getMonth(), 
      new Date(random_time_stamp).getFullYear()
    ];
  }

  function determineMonth(data) {
    const month = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"];
    return month[data[1]];
  }

  function randomNewBirthday() {
    let new_date = randomDateGen(startDate, endDate);
    let new_month = determineMonth(new_date);
    
    // Pad single digits
    let day = new_date[0] < 10 ? '0' + new_date[0] : new_date[0];
    let parsed_date = `${day} ${new_month} ${new_date[2]}`;

    box.innerText = parsed_date;
    birthday = parsed_date;
  }

  function yipee() {
    res.innerText = `Your birthday is on ${birthday}`;
  }

  window.addEventListener('load', (event) => { randomNewBirthday(); });
</script>