浏览器里timer所在的线程、event task runner以及主线程的关系

/**
if timer task runner is on another thread but main thread, 10s latter,
all the logs should be printed at once
otherwise, if timer task runner is inside main thread,
it has to wait for all the sync codes in a task to be
finished before checking the time and setting up the timer
related task, in which case the logs are printed one by
one(with 300ms time gaps in between) after 10s
*/
(function () {
    let n = 10;
    const timer = setInterval(function () {
        if (n--) {
            console.log(n);
            return;
        }
        clearInterval(timer);
    }, 300);
    const tenSecondsLatter = Date.now() + 10000;
    while(Date.now() < tenSecondsLatter) {}
    console.log('10s latter');
})();