JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.24.0/moment.min.js"></script>
<input type="date" id="date1" onchange='leavenumber();'/>
<input type="date" id="date2" onchange='leavenumber();'/>

JavaScript

var leavenumber = function(){
        var date1 = moment(document.getElementById("date1").value);
        var date2 = moment(document.getElementById("date2").value);
        if (date1.isValid() && date2.isValid()) {
           	console.log(date1.diff(date2, 'days'))
        }
       }