Learning JavaScript Design Patterns

The Mediator Pattern

The dictionary refers to a mediator as “a neutral party that assists in negotiations and conflict resolution.”^[2] In our world, a mediator is a behavioral design pattern that allows us to expose a unified interface through which the different parts of a system may communicate.

If it appears a system has too many direct relationships between components, it may be time to have a central point of control that components communicate through instead. The Mediator pattern promotes loose coupling by ensuring that instead of components referring to each other explicitly, their interaction is handled through this central point. This can help us decouple systems and improve the potential for component reusability.

A real-world analogy could be a typical airport traffic control system. A tower (mediator) handles which planes can take off and land, because all communications (notifications being listened for or broadcast) are performed from the planes to the control tower, rather than from plane to plane. A centralized controller is key to the success of this system, and that’s really the role that the Mediator plays in software design (Figure 9-5).

Figure 9-5. Mediator pattern

In implementation terms, the Mediator pattern is essentially a shared subject in the Observer pattern. This might assume that a direction Publish/Subscribe relationship between objects or modules in such ...