Signals vs RxJS

They are complementary, not rival teams.

Question	Signal	Observable
What is the current value?	natural	may require replay/current-value convention
Synchronous derivation	computed	operator pipeline works but may be heavier
Async sequence over time	limited alone	core strength
Cancellation/concurrency	not encoded by value	higher-order operators encode policy
Template read	call signal	AsyncPipe or bridge
Error/completion channels	no	yes
Dependency tracking	automatic on reads	explicit stream graph

Choose signals when

• state has a meaningful current synchronous value;
• UI derives values from other state;
• local/store updates are commands;
• fine-grained template consumption helps clarity.

Choose RxJS when

• multiple async events must be combined;
• cancellation, ordering, buffering, retries, or time matters;
• integrating router, forms, WebSocket, or HTTP streams;
• error and completion semantics are meaningful.

Bridge at ownership boundaries

Use toSignal when a component/store owns an observable and consumers need current state. Use toObservable when a signal must enter temporal operator composition. Avoid repeated back-and-forth conversion.

Common mistakes

• using an effect to copy one signal into another;
• subscribing inside subscribing instead of selecting flattening semantics;
• turning every event into a global subject;
• keeping server cache as an unbounded root signal without invalidation;
• claiming observables are obsolete because signals render conveniently.

Decision challenge

Before reading the example, classify completion percentage, typeahead requests, server cache, route parameters, and a websocket feed by owner, current-value semantics, time, error, completion, and concurrency needs. Implement one boundary in Signals and state and RxJS reasoning.

A strong explanation starts with semantics, not preference: “Completion percentage is synchronous derived state, so computed is appropriate. Typeahead requests require debounce and cancellation, so RxJS with switchMap expresses the policy. I bridge the result once into signal-based view state.”