JSFiddle - React, Tailwind, and code Playground

HTML

<input id="pagenumber" value="11" />
<div id="out">1</div>

JavaScript

var num = $('#pagenumber').val().toLowerCase();
var result = [0, 0].slice(0, num.length < 4 ? 3 - num.length : 0).join('') + num;
document.getElementById('out').innerHTML = result;