The .addItem() method is used to add new content to a custom menubar.
.addItem(item)
item
Required. This is the content of the menubar. It is derived from calling the NavBarMenuItem() function with the new keyword as the item argument.
This method is used to add new content to a custom menubar, by invoking the NavBarMenuItem() function. For examples on how to use it, refer to the Creating Custom Menubars section.