JSFiddle - React, Tailwind, and code Playground

HTML

<div id="result1"></div>
<div id="result2"></div>
<div id="result3"></div>

JavaScript

function isInteger(n) {
    return n % 1 === 0;
}

var result1 = isInteger(0.9);
document.getElementById('result1').innerHTML=result1;

var result2 = isInteger(0.9999999999999999);
document.getElementById('result2').innerHTML=result2;

var result3 = isInteger(0.99999999999999999);
document.getElementById('result3').innerHTML=result3;