paralleldrive/aidd-observe

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.

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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);

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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);

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Conversion helpers

| Helper | Usage | |--------|-------| | Observe.toPromise(obs) | Resolve with first value (one-shot) |

const first = await Observe.toPromise(service.states);

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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.

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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)