Design Patterns MCP Server

{ "id": "async-subject", "name": "AsyncSubject Pattern", "category": "Reactive", "description": "Subject that only emits the last value when the sequence completes", "when_to_use": "Single final result\nAsync operations\nPromise-like behavior", "benefits": "Single value emission\nCompletion-based\nPromise compatibility", "drawbacks": "No intermediate values\nCompletion dependency\nLimited use cases", "use_cases": "Single API calls\nFinal calculations\nPromise conversions", "complexity": "Medium", "tags": [ "reactive", "async", "completion" ], "examples": { "typescript": { "language": "typescript", "code": "// AsyncSubject: emit only last value on complete\nclass AsyncSubject<T> {\n private observers: Observer<T>[] = [];\n private value?: T;\n private hasValue = false;\n private completed = false;\n \n subscribe(observer: Observer<T>): Subscription {\n if (this.completed && this.hasValue) {\n observer.next(this.value!);\n observer.complete();\n } else if (this.completed) {\n observer.complete();\n } else {\n this.observers.push(observer);\n }\n \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 if (!this.completed) {\n this.value = value;\n this.hasValue = true;\n }\n }\n \n complete(): void {\n if (!this.completed) {\n this.completed = true;\n if (this.hasValue) {\n this.observers.forEach(obs => obs.next(this.value!));\n }\n this.observers.forEach(obs => obs.complete());\n }\n }\n}\n\n// Usage: Promise-like behavior\nconst result = new AsyncSubject<number>();\n\nresult.subscribe({ \n next: x => console.log('Result:', x), // Only called on complete\n error: () => {},\n complete: () => {} \n});\n\nresult.next(1);\nresult.next(2);\nresult.next(3);\nresult.complete(); // Emits 3 to all subscribers" } } }