JavaScript: disable <button> until value is selected

<form name="courseForm" id="courseForm">
    <select name="coursetype" id="coursetype">
        <option value="0" disabled>Select here...</option>
        <option value="1">CourseName 1</option>
        <option value="2">CourseName 2</option>
        <option value="3">CourseName 3</option>
    </select>
    <button type="button" id="startBtn" disabled>Start</button>
</form>

And do :

var courses = ['1','2']; // available courses

$('#coursetype').one('change', function() {
     $('#startBtn').prop('disabled', false);
});

$('#startBtn').on('click', function() {
    var val = $('#coursetype').val(),
        msg = $.inArray(val, courses) != -1 ? 'CourseName '+val+' is selected!' : 'This course is not implemented yet';
    alert(msg);
});

FIDDLE