Saratov64,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script>
window.addEventListener("DOMContentLoaded", function() {
var btn = document.querySelectorAll(".btn");
btn[0].addEventListener("click", function() {
clearInterval(timer);
timer = setInterval(station1, timeInterval)
});
btn[1].addEventListener("click", function() {
clearInterval(timer);
timer = setInterval(station2, timeInterval)
});
function station1() {
document.querySelector("#main").innerHTML += "1111 "
}
function station2() {
document.querySelector("#main").innerHTML += "2222 "
}
var timeInterval = 1E3;
var timer = setInterval(station1, timeInterval)
});
</script>
</script>
</head>
<body>
<div id="main"></div>
<input class="btn" name="" type="button" value="fn1">
<input class="btn" name="" type="button" value="fn2">
</body>
</html>