Suport for WeakRef / FinalizationGroup

[pocesar]

Search Terms

stage 3, tc39, weakref, finalization group

Suggestion

WeakRef and FinalizationGroup are Stage 3 https://github.com/tc39/proposal-weakrefs

Only drawback I could think of is that, implementing a polyfill would make it over engineered and less performant than the real thing (of course), and actually leak memory if not careful.

Use Cases

Key/value cache are a great example (as stated in the proposal itself)

Examples

// Fixed version that doesn't leak memory.
function makeWeakCached(f) {
  const cache = new Map();
  const cleanup = new FinalizationGroup(iterator => {
    for (const key of iterator) {
      // See note below on concurrency considerations.
      const ref = cache.get(key);
      if (ref && !ref.deref()) cache.delete(key);
    }
  });

  return key => {
    const ref = cache.get(key);
    if (ref) {
      const cached = ref.deref();
      // See note below on concurrency considerations.
      if (cached !== undefined) return cached;
    }

    const fresh = f(key);
    cache.set(key, new WeakRef(fresh));
    cleanup.register(fresh, key, key);
    return fresh;
  };
}

var getImageCached = makeWeakCached(getImage);

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

[RyanCavanaugh]

Generally we don't provide polyfills, just definitions. Since there's no definition here, the only thing that should happen is a lib update

[kitsonk]

This is closed but /lib/lib.esnext.weakref.d.ts still doesn't exist... It appears to be in src but is still being dropped somewhere in the build. Does an update to the LKG need to occur on master?

[K4rakara]

Can somebody please look into what @kitsonk mentioned?

Both WeakMap and WeakSet are defined, but not WeakRef.

[AgarwalPragy]

As of Jan 2021, WeakRef is now supported in Chrome, Firefox and Edge.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakRef

Typescript is still missing WeakRef.

Can we please reopen this issue?

[kitsonk]

@AgarwalPragy it is in TypeScript 4.1 and later: https://www.typescriptlang.org/play?target=99&ts=4.1.3#code/OoUwhg1gSiBmDcAoIA so the issue doesn't need to be re-opened.