The Line between the Proxy and Decorator Pattern

Differences between the Proxy and Decorator patterns

At this point in the course, we might have some legitimate doubts about the differences between the Proxy and the Decorator patterns. These two patterns are indeed very similar and they can sometimes be used interchangeably.

In its classic incarnation, the Decorator pattern is defined as a mechanism that allows us to enhance an existing object with new behavior, while the Proxy pattern is used to control access to a concrete or virtual object. There’s a conceptual difference between the two patterns, and it’s mostly based on the way they’re used at runtime.

We can look at the Decorator pattern as a wrapper; we can take different types of objects and decide to wrap them with a decorator to enhance their capabilities with extra functionality. A proxy, instead, is used to control the access to an object and it doesn’t change the original interface. For this reason, once we have created a proxy instance, we can pass it over to a context that expects the original object.

When it comes to implementation, these differences are generally much more obvious with strongly typed languages where the type of the objects we pass around is checked at compile time. In the Node.js ecosystem, given the dynamic nature of the JavaScript language, the line between the Proxy and the Decorator patterns is really blurry, and the two names are often used interchangeably. We have also seen how the same techniques can be used to implement both patterns.

When dealing with JavaScript and Node.js, our advice is to avoid getting bogged down with the nomenclature and the canonical definition of these two patterns. We encourage you to look at the class of problems that Proxy and Decorator solve as a whole and treat these two patterns as complementary and sometimes interchangeable tools.