WeakRef : Object

A WeakRef allows holding on to another object, while still allowing that object

to be garbage collected if there are no other strong references to it. Note,

JavaScript makes no guarantees on if or when an object will be garbage collected.

See also %%/FinalizationRegistry|FinalizationRegistry%%.

Spec:

https://tc39.es/ecma262/#sec-weak-ref-objects

Version:

ECMAScript 2021

----

new WeakRef(target : Object) : WeakRef

Creates a new WeakRef that tracks **target**.

Spec:

https://tc39.es/ecma262/#sec-weak-ref-target

----

prototype.deref() : Object

Returns the target of **this** if it has not been garbage collected yet, otherwise

returns **undefined**. If **deref()** returns a valid object, that object

will not be garbage collected until control returns to the event loop, such as

when returning from a callback or **await**ing a %%/Promise|Promise%%.

<example>

const sleep = (ms) => new Promise(r => setTimeout(r, ms));

let foo = {};

const weakRef = new WeakRef(foo);

foo = undefined; // Clear strong reference

const startTime = Date.now();

console.log('Allocating a lot of objects to force garbage collection');

while (weakRef.deref()) {

for (let i = 0; i < 100; i++) {

const x = new Array(100);

}

await sleep(10);

}

console.log(`foo was reclaimed after ${((Date.now() - startTime) / 1000).toFixed(1)}s`);

</example>

Spec:

https://tc39.es/ecma262/#sec-weak-ref.prototype.deref