lookat

LookAt

An observer/observable library

API

Observable

const counter = observable(0); // returns counter.$ ($ is the reactive value accessor making the reactivity explicit in the naming). To mutate, use counter.$++ for example const person = observable({ firstname: "Ayoub", age: 28 }); // returns counter.$.age...

Observe

const voidValue = observe(() => console.log(counter * 2)); // side effects const isPair = observe(() => counter % 2 === 0); // computed reactive value => returns observable value observe(() => { console.log(isPair.$) })

Utilities

unwrap(isPair) // returns raw value of an observable

TODO

• Enable object like observable source
• [x] Enable Array observable source
• [ ] Enable Map observable source
• [ ] Enable Set observable source
• [x] Enable delete operator and other missing trap operators
• [x] Do not call observers if impacted value is not modified (check inside the setter trap)
• Batch observer calls:
  • Avoid multiple same consecutive observable updates to trigger multiple observer calls (it should call one time): const counter = observable(0); const handleAdd = () => { <- Should be batched counter.$++; counter.$++; } observe(() => { counter.$ // <- Should be called one time and not two })
  • Optimize same observer calls if the side effect relies on computed observables const counter = observable(0); const counterSquare = observe(() => counter.$2); observe(() => { console.log("Counter Quatro = ", counter.$, " ", counterSquare.$); }); // => Currently, it's called two times since the observer relies on two observables but it could be improved with some predicates to be called once
• [ ] Performance/Memory benchmark
• Readme + Hosted documentation

Notes

Direct access via counter instead of counter.$ and non reactivity inside observe callback

API limitations and caveats with object like observable:

👉 Updates are always notified from top to bottom. Updating a child property won't notify its parent observers. But a parent update (such a new reference through object affectation) will notify its child property observers. And it's quite natural and aligned with JS runtime: => value and reference are managed from top to bottom: a child cannot update its parent reference.

👉 Parent update (eg. new object affectation) will notify its child observers if and only if all accessors to reach the targetted child property are specified inside the observe callback:

❌ const state = person.$ ❌ observe(() => { state.firstName }) ❌ person.$ = { firstName: "New" } ❌ // The observe callback won't be called

✔️ observe(() => { person.$.firstName }) ✔️ person.$ = { firstName: "New" } ✔️ // The observe callback will be called