Design Patterns

Pattern interviews test recognition of recurring structure and judgment about cost—not Gang of Four trivia. Explain what problem a pattern solves, what it costs, and what you would use instead in a small codebase.

Coverage includes creational, structural, and behavioral GoF patterns plus frontend (container/presentational, compound components, hooks reuse) and backend patterns (repository, unit of work, service layer, DTO, DI, middleware).

On interviews: name the pattern, draw the roles briefly, and say when you would not introduce it.

Common pitfalls: pattern obsession, confusing similar patterns (strategy vs state), and patterns without a clear variation point.

Checklist:

• Start from the variation or extension need.
• Compare pattern cost to a simpler function or module.
• Map pattern to a library or framework you have used.
• Mention testability impact.