What are your most used design patterns?

Publisher/subscriber and composite patterns had the greatest impact on the quality of my code, apps that are composited from small decoupled parts are much easier to reason about.<p>I'm also using delegate and prototype patterns a lot, though those are rather dangerous when misused. Deep inheritance chains or excessive method overrides can easly make the code unmaintainable.

I get a lot of mileage out of the delegate pattern. We used visitor exactly once in our codebase, but it's pretty fantastic for that one place it's needed. We use observer extensively. More than other patterns that one strikes me as something the language should do for me.

I suspect that the most used pattern in the HN community is the ActiveRecord pattern although many who use it probably are not aware that they are doing so.

Service Layer, Repository, Unit of Work. Those are the first I can think of (and use very often).

In JavaScript I'd say I use the module pattern and prototype pattern the most.

Composed Method.