onBeforeContextMenu

fires before the context menu is called in the item area

function onBeforeContextMenu(
    // the id of the clicked item
    id: string,
    // a native event object
    e: Event,
    // the target HTML element
    node: HTMLElement
): boolean

Returns

boolean returning false will block the event

Example

grid.attachEvent("onBeforeContextMenu", function(id, e, node){
     if (some_check(id))
          return false; // blocks the context menu
     else
          return true;
});

Details

Returning false from the event handler will block further processing.