JSFiddle - React, Tailwind, and code Playground

JavaScript

function doStuff(callback) {
        setTimeout(function () {
            for (var i = 0; i < 1000; i++) {
                // do some busy work
                var x = Math.sqrt(i);
            }
    
            callback();
        }, 0);
    }
    
    console.log('start');
    doStuff(function () {
        console.log('callback called');
    });
    console.log('after doStuff()');