Passing Data Between Components Summary
In the above sections we have seen 2 ways to pass data between components using the
= to pass variables from the current component into the component.
& to register a callback for component to invoke (with data if necessary) in order to pass data out of the component.
& are the mechanism that allow our component to have a "public API".
Note, if the attribute name and the property of the component class match the name can be omitted. i.e instead of
username: '=username' we can just write
username: '=', with the same shortcut applying to