The snippet code below shows how to add a menu, My Menu, in WebGrid’s row context menu.

function WebGrid1_OnRowContextMenu(controlId, rowType, rowElement, menuObject) {
    var separator = new WebMenuItem();
    separator.Type = "Separator";
    separator.Name = "MySeparator";

    var menuItem = new WebMenuItem();
    menuItem.Text = "View Row's KeyValue";
    menuItem.Name = "MyMenu";
    menuItem.OnClick = "RowKeyValue";

    //Add Menu Separator and Menu Item
    menuObject.Items.Add(separator);
    menuObject.Items.Add(menuItem);

    return true;
}

function RowKeyValue() {
    var WebGrid1 = ISGetObject("WebGrid1");
    var key = WebGrid1.GetSelectedObject().GetRowObject().KeyValue;

    alert(key);

    return true;
}

The complete sample is enclosed as attachment. Hope this helps.

thank you