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. --- ## 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 | ```ts 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 | ```ts 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) | ```ts const first = await Observe.toPromise(service.states); ``` --- ## Common patterns **Derived observable from service:** ```ts export const isDevelopment = memoize((service: Pick<EnvironmentService, 'type'>) => Observe.withMap(service.type, type => type === 'development') ); ``` **Computed from multiple resources:** ```ts 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 ```sudolang 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](../aidd-service/SKILL.md) — Observe in front-end services (data up via Observe)