$(document).ready(function() {
    $("#subscribeButton").click(function() {
        var $inputValue = $("#emailfield").val();
        if ($inputValue) {
            $.ajax({
			    type: "POST",
			    url: "ajax_subscribe.php",
			    data: 	"email=" + $inputValue,
			    success: function(html) {
				    $("#subscribe").html(html);
			    }
		    });
        }
    });
});