Design Patterns MCP Server

{ "id": "cold-observable", "name": "Cold Observable Pattern", "category": "Reactive", "description": "Observable that starts emitting values only when subscribed to", "when_to_use": "On-demand data\nIndependent streams\nHTTP requests", "benefits": "On-demand execution\nIndependent streams\nResource control", "drawbacks": "Multiple executions\nResource duplication\nTiming differences", "use_cases": "HTTP requests\nFile reads\nDatabase queries", "complexity": "Low", "tags": [ "reactive", "cold", "on-demand" ], "examples": { "typescript": { "language": "typescript", "code": "// Cold Observable: separate execution per subscriber\nclass ColdObservable<T> {\n constructor(\n private producer: (observer: Observer<T>) => () => void\n ) {}\n \n subscribe(observer: Observer<T>): Subscription {\n const teardown = this.producer(observer);\n return { unsubscribe: teardown };\n }\n}\n\n// Usage: HTTP request (new request per subscriber)\nconst httpRequest = new ColdObservable<Response>(observer => {\n const controller = new AbortController();\n \n fetch('https://api.example.com/data', { \n signal: controller.signal \n })\n .then(response => {\n observer.next(response);\n observer.complete();\n })\n .catch(error => observer.error(error));\n \n return () => controller.abort();\n});\n\n// Each subscriber triggers a new HTTP request\nhttpRequest.subscribe({ next: r => console.log('Sub 1:', r), error: () => {}, complete: () => {} });\nhttpRequest.subscribe({ next: r => console.log('Sub 2:', r), error: () => {}, complete: () => {} });" } } }