gistfile1.js

WebserviceCall = function () {
    {
        var enable = true;
        var listId = SP.ListOperation.Selection.getSelectedList();
        var items = SP.ListOperation.Selection.getSelectedItems();
        if (items.length == 0)
            return false;

        var selectedIds = new Array();

        for (var i in items) {
            selectedIds.push(parseInt(items[i].id));
        }
        //The list id is a GUID string like, i.e. "{77c51b5a-fb48-4228-8c92-ee5834d7fefc}"
        var data = { selectedIds: selectedIds, listId: listId };

        jQuery.ajax({
            url: "/sites/docs/_vti_bin/RibbonMethods.asmx/IsAnyDocumentScheduled",
            type: "POST",
            dataType: "json",
            data: JSON.stringify(data), async: false,
            success: function (result, status) {
                enable = result.d;
            },
            error: function (jqXHR, textStatus, errorThrown) {
                MS.InformationManagement.Common.ShowStatus(jqXHR.responseText, 'red', 6000);
                enable = false;
            },
            contentType: "application/json; charset=\"utf-8\""
        });
        return enable;
    }
}