10 Design Patterns Explained in 10 Minutes

Software design patterns matter because they offer reusable, language-aware ways to solve recurring problems—without turning every solution into copy-paste boilerplate. The core takeaway is that patterns are not a checklist to memorize; they’re tradeoffs. Used well, they reduce complexity and improve maintainability. Used blindly, they add ceremony, indirection, and extra code that future maintainers must untangle.

The tour starts with creational patterns. Singleton restricts a class so only one instance exists—implemented in TypeScript by making the constructor private and exposing a static instance getter. But the discussion quickly turns practical: in JavaScript, global objects and reference semantics can mimic “single instance” behavior with less boilerplate, so the pattern’s value depends on the language’s built-in capabilities.

Prototype reframes inheritance as cloning from an existing object rather than extending a class hierarchy. In JavaScript’s prototypal model, creating a new object from a prototype (e.g., via object creation using the prototype object) keeps the prototype chain flat and lets shared behavior resolve dynamically. The example highlights how properties may appear missing when inspected, yet methods still work because lookups walk up the prototype chain. The notes also flag that relying on older prototype access patterns (like direct proto access) is discouraged in modern JavaScript.

Builder and Factory address object construction complexity. Builder breaks large constructor parameter lists into step-by-step configuration, often enabling method chaining by returning this. It’s common in libraries such as jQuery, though it has fallen out of fashion in some modern codebases. Factory replaces repeated conditional instantiation logic with a single function that chooses which concrete object to create—illustrated with a cross-platform iOS/Android UI scenario where one interface needs different button implementations.

Structural patterns focus on organizing relationships between components. Facade provides a simplified API that hides internal subsystems—like combining plumbing and electrical operations behind one “turn on/off” method—so consumers don’t need to understand low-level details. Proxy acts as a stand-in for another object, with a concrete example in Vue.js reactivity: the framework intercepts property access and updates via proxy handlers (get/set), triggering UI renders while letting developers interact with the proxy as if it were the original object.

Behavioral patterns cover coordination and control flow. Iterator defines how to traverse a collection, and the transcript uses a custom JavaScript iterator with a next method and a done flag, then ties it to Symbol.iterator so it can work with a regular for...of loop. Observer is push-based: multiple subscribers react when a subject emits new values, with Firebase-style real-time updates and an RxJS subject example. Mediator reduces dangerous many-to-many communication by routing interactions through a central coordinator—compared to Express.js middleware, which intercepts requests and transforms them into responses.

The final pattern, State, replaces sprawling switch statements with state-specific behavior. An object delegates an identical method to different state classes (or state implementations) depending on its current finite state, keeping the public API stable while making behavior predictable. The overall message: design patterns are powerful tools, but the best choice is contextual—shaped by the language, the problem, and the cost of added abstraction.