On the PHP-Tip-a-Day site today there's an new "fable" posted in the Design Pattern Fables series. This time it's about the Observer pattern (and kings and princes).

The first place I recall encountering the observer pattern was not in PHP, but in JavaScript. If you've ever set a listener to fire when an event happened, you've used the observer pattern. Functions or methods are registered with an object so that when it experiences a specific event, it "notifies" the registered functions or methods by calling them.

His story tells about a royal family, a pregnancy and magic mirrors that allows for instant communication between the family and outlying locations. He relates it to the objects and "watchers" that make up the Observer pattern and gives a brief code example (in Javascript) of a HTML button and a jQuery event observer that fires when it's clicked.