document.getElementById('weeklySelect').value code example

Example: how to use document.getelementbyid

<p id="YourId">How to use document.GetElementById in HTML</p>
<script>
  function demo(){
document.GetElementById('YourId')./* The thing you need to do to your code... Here I want .innerHTML you can take any...  */.innerHTML('/* what will it change... */')
  }
</script>
<!-- Now execute it by writing the button tag!--><button onclick="demo()">Click Me!!!</button>