using pre-trigger to validate the properties of an azure Cosmos DB item that is being created

function HolidayTip() {
    var r = getContext().getRequest();

    // item to be created in the current operation
    var it = r.getBody();

    // validate properties
    if (!("holidaytip" in it)) {
        it[tip]=0;
    }

    // update the item that will be created
    r.setBody(it);
}