To make a drop down menu in JavaScript, create a 
select element with a bunch of option's.So if this is your container element, that will hold your drop down menu:
<div id="my-container"></div>
Then you can make a drop down menu inside of it with this JavaScript:
document.getElementById("my-container").innerHTML = `
  <select>
    <option value="1">Option 1</option>
    <option value="2">Option 2</option>
    <option value="3">Option 3</option>
  </select>
`;
