how to us etime intervals in javascript code example

Example 1: javascipt delay

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

console.log("Hello");
sleep(2000).then(() => { console.log("World!"); });

Example 2: onclick timer javascript

document.getElementById("gameStart").addEventListener("click", function(){
    var timeleft = 15;

    var downloadTimer = setInterval(function function1(){
    document.getElementById("countdown").innerHTML = timeleft + 
    " "+"seconds remaining";

    timeleft -= 1;
    if(timeleft <= 0){
        clearInterval(downloadTimer);
        document.getElementById("countdown").innerHTML = "Time is up!"
    }
    }, 1000);

    console.log(countdown);
});