Edit in JSFiddle

var add;
var input = document.getElementById("input");

function start() {
    add = setInterval(function() {
        input.val++;
    }, 1000);
}

function stop() {
    clearInterval(add);
}

$('#start').click(start);
$('#stop').click(stop);

start();
<input type="number" id="input" />
<input type="button" id="stop" value="stop"/>
<input type="button" id="start" value="start"/>