Design Patterns MCP Server

{ "id": "behavior-subject", "name": "BehaviorSubject Pattern", "category": "Reactive", "description": "Subject that requires initial value and emits current value to new subscribers", "when_to_use": "State management\nCurrent value access\nInitial state", "benefits": "Current value access\nState preservation\nImmediate emission", "drawbacks": "Memory overhead\nState management complexity\nInitial value requirement", "use_cases": "Application state\nUser preferences\nConfiguration", "complexity": "Medium", "tags": [ "reactive", "state", "behavior-subject" ], "examples": { "typescript": { "language": "typescript", "code": "// BehaviorSubject: subject with current value\nclass BehaviorSubject<T> {\n private observers: Observer<T>[] = [];\n \n constructor(private value: T) {}\n \n subscribe(observer: Observer<T>): Subscription {\n observer.next(this.value); // Emit current value immediately\n this.observers.push(observer);\n return {\n unsubscribe: () => {\n const index = this.observers.indexOf(observer);\n if (index > -1) this.observers.splice(index, 1);\n }\n };\n }\n \n next(value: T): void {\n this.value = value;\n this.observers.forEach(obs => obs.next(value));\n }\n \n getValue(): T {\n return this.value;\n }\n}\n\n// Usage: State management\nconst currentUser = new BehaviorSubject<string | null>(null);\n\n// New subscriber gets current value immediately\ncurrentUser.subscribe({\n next: user => console.log('User:', user), // Logs: null\n error: () => {},\n complete: () => {}\n});\n\ncurrentUser.next('john@example.com'); // Logs: john@example.com" } } }