var re=/^[A-Z]/;
alert(re.test('a'));
alert(re.test('A'));

<input type="text" />
<script>
    document.querySelector('input').onchange = function() {
        var str = this.value; 
        alert('Первая большая? ' + (str[0] == str[0].toUpperCase()));
    }
</script>

<script>
$('#EmployeeID').on('input', function () {

	var ln = $('#EmployeeID').val().length;
	var pr = $('#EmployeeID').val().charAt(0);
	if(ln == '6' && pr == 'S'){
	alert("YES");
	}else{
	alert("NO");
	}

});
</script>