Design Patterns for Node.js Applications
Named, reusable solutions to problems that recur when you structure real code
- recognise and write six patterns idiomatically in JavaScript -- factory, singleton, strategy, observer, adapter, and dependency injection;
- say when each pattern earns its keep and when it merely adds ceremony;
- refactor a tangled module into small collaborators that are easy to test;
- avoid the classic trap of applying patterns everywhere ("pattern soup").
1. What a pattern is -- and when it over-engineers
Patterns are descriptions, not code. The same pattern looks different in Java (heavy classes and interfaces) than in JavaScript, where functions are values and objects are dynamic. In Node the idiomatic form is often smaller than the textbook version: a factory can be a plain function, a strategy can be a function in a lookup table, an observer is usually just an EventEmitter.
The honest caveat comes first: a pattern applied to a problem you do not have is a cost, not a benefit. Every layer of indirection you add makes the code harder to read for the next person. Reach for a pattern when it removes real, present pain -- duplicated construction logic, an untestable class, a swelling if/else that changes every sprint -- not because a diagram looked clever. "You aren't gonna need it" (YAGNI) beats speculative abstraction almost every time.
Analogy. Patterns are like knots a sailor knows by name. A skilled sailor does not tie every knot on every rope; they pick the bowline when they need a fixed loop and nothing when a rope just needs coiling. The value is in recognising the situation, not in showing off the knot.