paralleldrive Observe pattern
Observe<T> from @adobe/data/observe — a subscription function: (notify: (value: T) => void) => Unobserve. Callback may be invoked synchronously or asynchronously, zero or more times. Returns Unobserve to stop observing.
Creation helpers
| Helper | Usage |
|---|---|
Observe.fromConstant(value) |
Observe<T> from a constant value |
Observe.fromProperties({ a, b }) |
Combine named observables into Observe<{ a, b }> |
Observe.fromArray([obs1, obs2]) |
Combine array of observables into Observe<T[]> |
Observe.fromPromise(() => Promise) |
Lazy; notifies once when promise resolves |
Observe.createState(initial?) |
[Observe<T>, (value: T) => void] — mutable state |
const constant = Observe.fromConstant(42);
const combined = Observe.fromProperties({ a: db.observe.resources.a, b: db.observe.resources.b });
const [count, setCount] = Observe.createState(0);
Transformation helpers
| Helper | Usage |
|---|---|
Observe.withMap(obs, fn) |
Transform value; map from one type to another |
Observe.withFilter(obs, fn) |
Transform or filter; return undefined to skip |
Observe.withDefault(default, obs) |
Use default when value is undefined |
const doubled = Observe.withMap(count, n => n * 2);
const isDev = Observe.withMap(service.type, t => t === 'development');
const max = Observe.withFilter(
Observe.fromProperties({ a, b }),
({ a, b }) => Math.max(a, b)
);
const withFallback = Observe.withDefault('unknown', maybeName);
Conversion helpers
| Helper | Usage |
|---|---|
Observe.toPromise(obs) |
Resolve with first value (one-shot) |
const first = await Observe.toPromise(service.states);
Common patterns
Derived observable from service:
export const isDevelopment = memoize((service: Pick<EnvironmentService, 'type'>) =>
Observe.withMap(service.type, type => type === 'development')
);
Computed from multiple resources:
Observe.withFilter(
Observe.fromProperties({ a: db.observe.resources.a, b: db.observe.resources.b }),
({ a, b }) => Math.max(a, b)
);
Lazy creation: Observe.withLazy(() => expensiveObs) — defers until first subscription.
Execute
fn whenAddingOrUsingObserve() {
Constraints {
Use Observe.fromConstant for static values
Use Observe.fromProperties to combine multiple observables
Use Observe.withFilter when mapping and/or filtering
Use Observe.createState for mutable state with a setter
Call unobserve() when cleaning up (e.g. component unmount)
}
}
Related
- service — Observe in front-end services (data up via Observe)