implementation-design-patterns

A TypeScript guide to the 22 Gang of Four design patterns, which are named ways to structure recurring software-design problems. Each pattern includes examples, when to use it, and when it would add unnecessary complexity.

In plain words
What is it for?
Use it when designing, refactoring, or reviewing TypeScript modules involving interchangeable implementations, incompatible APIs, tree-shaped data, or growing class hierarchies.
Why use it?
It helps replace tangled inheritance, type-based conditionals, tight coupling, and classes with too many responsibilities with a fitting structure.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/pproenca/dot-skills/implementation-design-patterns
Any agent
npx skills add pproenca/dot-skills --skill implementation-design-patterns
Clone the repo
git clone --depth 1 https://github.com/pproenca/dot-skills

Made for: Claude Code, Codex.

Per session 202 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,512 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00202 $0.02512
Opus 5 $0.00101 $0.01256
Sonnet 5 $0.00040 $0.00502
Haiku 4.5 $0.00020 $0.00251

Measured yesterday against content hash ec0eb3266ff3, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

implementation-design-patterns scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/.curated/implementation-design-patterns/SKILL.md · 95 lines

How it starts

The opening of the file, as written. The whole thing — 95 lines — stays where its author put it; the contents beside it link to each section on GitHub.

TypeScript Design Patterns Best Practices (Refactoring Guru)

Implementation reference for the 22 Gang of Four design patterns in TypeScript, distilled from refactoring.guru. Each of the 22 pattern files across 3 categories captures intent, problem, solution, applicability, a runnable TypeScript example, implementation steps, pros/cons, and relations to sibling patterns.

The patterns are a vocabulary for structural decisions, not a prescription. Reach for a pattern only when its applicability criteria match the problem at hand — every pattern entry includes a When NOT to Use section to guard against over-engineering.

When to Apply

  • Refactoring a class that has grown unwieldy via inheritance — combinatorial subclasses, conditional branching on type, or a "god class" with many responsibilities
  • Designing a new module whose collaborators are not yet fixed — you want to keep the interface stable while implementations vary
  • Integrating an incompatible third-party API, library, or legacy class into existing code
  • Modeling a tree-shaped domain (file systems, organization charts, expression ASTs, UI component trees) where leaves and branches must be treated uniformly
  • Adding cross-cutting behavior at runtime — logging, caching, access control, decoration — without subclassing
  • Selecting an algorithm or behavior variant at runtime based on configuration, user input, or environmental conditions
  • Implementing undo/redo, history snapshots, transactional rollback, or scheduling/queueing of operations
  • Coordinating many objects whose direct mutual references have become tangled — a hub that brokers communication
  • Notifying many subscribers when something changes — event systems, reactive data flows
  • Reviewing code that smells like a pattern is implicit (large switch on kind, parallel class hierarchies, identical algorithm skeletons across siblings) — make it explicit

Rule Categories

# Category Impact Patterns When to reach for this group
1 Creational HIGH 5 Object construction is non-trivial, varies by configuration, or risks tight coupling to concrete classes
2 Structural HIGH 7 Composing classes/objects into larger structures while keeping parts substitutable
3 Behavioral HIGH 10 Distributing responsibility and defining how objects collaborate at runtime

Read the full file on GitHub · 95 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 95 lines · 202 tokens per session scan A ec0eb3266ff3

Subscribe to this mod's changes

implementation-design-patterns is a skill published in the GitHub repository pproenca/dot-skills (200 stars, last pushed 16d ago), licensed MIT. It adds 202 tokens to every session and 2,512 once invoked, about $0.0010 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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