Support Callback Functions for Submenus

[nkappler]

I was expecting this modified example to do what you want:

ctxmenu.attach("#body", [
            {
                text: "Parent",
                subMenu: function beforeOpenSubMenu() {
                    alert("beforeOpenSubmenu");

                    return [
                        {
                            text: "child",
                            action: (event) => {
                                const childListElement = event.target.parentElement;
                                const submenu = childListElement.parentElement;
                                const parentListElement = submenu.parentElement;
                                console.log(parentListElement.querySelector("span").innerText);
                            }
                        }
                    ];
                }
            }
        ], function beforeOpen(menu) {
            alert("BeforeOpen")

            return menu;
        });

You can pass a function as a third parameter to the attach method, which will be called before the root menu opens.
Note that the function receives the menu definition as a parameter and also has to return it.
You can modify it as you please, but this function needs to return a valid menu definition.

As per my own documentation, you should also be able to pass a function to generate the submenu (beforeOpenSubMenu), however the Parent list item ends up being disabled.
It's been a while that I wrote this code and honestly the test coverage is at best mediocre, since it depends on manual testing,
but I am pretty sure that this is a bug.

The beforeOpenSubMenu should be called just before the submenu is being opened, but currently it is never called.
I've created a new bug #45 to track this.

Originally posted by @nkappler in #44 (comment)