JSFiddle - React, Tailwind, and code Playground

HTML

<h1 id="title">undefined date </h1>

<input type="submit" id="byBtn" value="Change" onclick="change2()"/>

JavaScript

function change2()
{
  
     // Attempt to insert text at the cursor position. If insertion returns null,
    // then the cursor's containing element doesn't allow text insertions.
    var month = ["JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC"];
    
    var d = new Date();
    var dd = d.getDate();
    dd = pad(dd, 2);
   
    var mm = d.getMonth();
 
    var yyyy = d.getFullYear();
    var datec = dd + "-" + month[mm] + "-" + yyyy;
    
    alert(datec);//without pad
    mm = pad(mm,2);

    var datec = dd + "-" + month[mm] + "-" + yyyy;
    alert(datec);//with pad
}

function pad(str, max) {
    str = str.toString();
    return str.length < max ? pad("0" + str, max) : str;
}