How to add onClick event to PopupMenuBarItem in Dojo?

I can’t figure out how to add an onclick event to a menu item, please help me solve this problem.

<script>
    require([
        "dijit/MenuBar",
        "dijit/PopupMenuBarItem",
        "dijit/Menu",
        "dijit/MenuItem",
        "dijit/DropDownMenu",
        "dojo/domReady!"
    ], function(MenuBar, PopupMenuBarItem, Menu, MenuItem, DropDownMenu){
        var pMenuBar = new MenuBar({});

        var pSubMenu = new DropDownMenu({});
        pMenuBar.addChild(new PopupMenuBarItem({
            label: "ItemMenu1",
            popup: pSubMenu
        }));

        var pSubMenu2 = new DropDownMenu({});
        pMenuBar.addChild(new PopupMenuBarItem({
            label: "ItemMenu2",
            popup: pSubMenu2,
        }));

        pMenuBar.placeAt("navigation");
        pMenuBar.startup();
    });
</script>

I added onClick to the code using this method, but it doesn’t work.

var pSubMenu = new DropDownMenu({});
pMenuBar.addChild(new PopupMenuBarItem({
    label: "ItemMenu1",
    popup: pSubMenu,
    onClick: function () {alert('ItemMenu1');}
}));