creating a stopwatch using javascript

Question

I'm learning how to code and decided to try out this project which is creating a stopwatch using javascript but can't seem to get my code working. The buttons still remain unresponsive. Any help would be appreciated.I've posted snippet of the javascript code below

window.onload = function () {
    var btnStart = document.getElementById("btn-start");
    var btnStop = document.getElementById("btn-stop");
    var btnRestart = document.getElementById("btn-restart");
    var secs = 00;
    var tens = 00;


    var appendSecs = document.getElementById("secs");
    var appendTen = document.getElementById("ten");

    var timeInterval;

    function startWatch() {
        tens++;
        if (tens < 9) {
            appendTen.innerHTML = '0' + tens;
            appendSecs.innerHTML = '00';
        }
        else if (tens > 9) {
            appendTen.innerHTML = tens;
            appendSecs.innerHTML = '00';
        }
        else if (tens > 99) {
            secs++;
            appendSecs.innerHTML = '0' + secs;
            appendTen.innerHTML = "00";
        }
        else if (secs < 9) {
            secs++;
            appendSecs.innerHTML = "0" + secs;
            appendTen.innerHTML = "00";
        }
    }
    function start() {
        timeInterval = setInterval(startWatch(), 10);
    }

    function restart() {

        clearInterval(timeInterval);
        appendSecs.innerHTML = 00;
        appendTen.innerHTML = 00;
    }


    function stop() {
        clearInterval(timeinterval);
    }
    btnStart.addEventListener("click", start());
    btnRestart.addEventListener("click", restart());
    btnStop.addEventListener('click', stop())
}