JSFiddle - React, Tailwind, and code Playground

HTML

<input type="button" onclick="performSlowSyncronousRequest()" value="Sync test-case"/>

JavaScript

function performSlowSyncronousRequest() {
    var endsIn, initial;

    delay = 5000;

    endsIn = new Date().getTime() + delay;

    for (; endsIn >= new Date().getTime();) {}//Delay
    window.open('http://www.thirtykingdoms.com');
}