JSFiddle - React, Tailwind, and code Playground

HTML

<div id="console"></div>

CSS

#console {
    background: #f4f4f4;
    color: #444;
    font-family: arial, sans-serif;
    font-size: 14px;
    line-height: 16px;
    padding: 15px;
    max-width: 400px;
}

JavaScript

var thenum = [5, 3, 678, 213];

function max(num){
    return Math.max.apply(null, num);
}

document.getElementById('console').innerHTML = '<p>max([' + thenum.join(', ') + '])= ' + max(thenum) + ';</p>';

Array.prototype.max = function () {
    return Math.max.apply(null, this);
};

document.getElementById('console').innerHTML += '<p>[' + thenum.join(', ') + '].max()= ' + thenum.max() + ';</p>';