Restart Timer/Countdown from Start on Click

I have been trying to restart Countdown on Click but didnot find any Solution.
How to achieve it?

What i am trying to achieve is When user click next button Countdown should restart from “GetReady” not from where it stopped previously.

var countDown = 42;
var counter = [ 'GetReady','10','9','8','7','6','5','4','3','2','1','LetsGo','30','29','28','27','26','25','24','23','22','21','20','19','18','17','16','HalfWay','14','13','12','11','10','9','8','7','6','5','4','3','2','1','Done'];
var urlToCount = new Observable ('Get Ready');

function changeCountdown() {
            countDown += 1;
            if (countDown >= counter.length) {
                countDown = 0;
            urlToCount.value = counter[countDown];
        }  var Clockinterval = setInterval(changeCountdown, 1000);

function RestartCountdown() {
                setInterval(changeCountdown, 1000);

Maybe in the RestartCountdown function, you have to reset your countDown variable back to 42