JSFiddle - React, Tailwind, and code Playground

HTML

<body>

<p>Date values before assignment.</p>
<p id="beforeassign1"></p>
<p id="beforeassign2"></p>
<p id="beforeassign3"></p>
<p>Date values after assignment with setdate(date2 only assigned).</p>
<p id="afterassign1"></p>
<p id="afterassign2"></p>
<p id="afterassign3"></p>


</body>

JavaScript

var date1 = new Date();
var date2 = new Date(1991,4,11);
var date3 = new Date(1992,4,11);
document.getElementById("beforeassign1").innerHTML = date1.toDateString();
document.getElementById("beforeassign2").innerHTML = date2.toDateString();
document.getElementById("beforeassign3").innerHTML = date3.toDateString();
date3 = new Date(date1);
date2 = new Date(date1);
date2.setDate(date2 .getDate() + 40);
document.getElementById("afterassign1").innerHTML = date1.toDateString();
document.getElementById("afterassign2").innerHTML = date2.toDateString();
document.getElementById("afterassign3").innerHTML = date3.toDateString();