JSFiddle - React, Tailwind, and code Playground

HTML

<div id='mydiv'><div class='myclass'></div></div>

JavaScript

var start = (new Date()).getTime();
for (var i=0;i<100000;i++) {
    //var x = $('.myclass', '#mydiv');
    //var x = $('#mydiv').find('.myclass');
    var x = $('#mydiv .myclass');
    //var x = $('#mydiv div.myclass');
}
var end = (new Date()).getTime();

$('body').append('<div>'+(end-start)+'</div>');