<!DOCTYPE html>
<html lang="en">
<head>
</head>
<body>
<div class="form_element_control">
<input type="submit" class="btn btn-primary" value="Отправить">
</div>
<script>
function func(){
alert('Конверсия!!');
}
document.querySelector('.btn-primary').addEventListener("click", func, false);
</script>
</body>
</html>