Widely available Use only for advanced caching or integration scenarios where ordinary strong references create real memory pressure.

Weak references

A FinalizationRegistry object lets you request a callback when a value is garbage-collected.

MemoryWeakRefCleanup

Browser support

Feature Desktop Mobile
Chrome
Edge
Firefox
Safari
Chrome Android
Safari iOS
FinalizationRegistry
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FinalizationRegistry.FinalizationRegistry

The FinalizationRegistry() constructor creates FinalizationRegistry objects.
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FinalizationRegistry.register

The register() method of FinalizationRegistry instances registers a value with this FinalizationRegistry so that if the value is garbage-collected, the registry's callback may get called.
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FinalizationRegistry.register.symbol as target

Non-registered symbol as target
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FinalizationRegistry.unregister

The unregister() method of FinalizationRegistry instances unregisters a target value from this FinalizationRegistry.
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FinalizationRegistry.unregister.symbol as target

Non-registered symbol as target
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Other
javascript.builtins.WeakRef

A WeakRef object lets you hold a weak reference to another object, without preventing that object from getting garbage-collected.
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Built-in object
WeakRef.WeakRef

The WeakRef() constructor creates WeakRef objects.
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WeakRef.WeakRef.symbol as target

Non-registered symbol as target
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WeakRef.deref

The deref() method of WeakRef instances returns this WeakRef's target value, or undefined if the target value has been garbage-collected.
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1+Supported (version) Not supported ※Has note Sub-feature descriptions sourced from MDN Web Docs (CC BY-SA 2.5)

Syntax

JAVASCRIPT 
let target = { data: 'important' };
const ref = new WeakRef(target);

ref.deref(); // { data: 'important' }
target = null; // Becomes a candidate for garbage collection
// ref.deref(); // undefined (after garbage collection)

Live demo

Create and dereference a WeakRef

Wrap an object in WeakRef and inspect the current dereferenced value.

JavaScript
Output
Press the Run button

Use WeakRef in a cache

Keep a lightweight reference in a cache without forcing long-term retention.

JavaScript
Output
Press the Run button

Compare direct objects and WeakRef

See the difference between the original object and its weak reference wrapper.

JavaScript
Output
Press the Run button

Use cases

  • Opportunistic caches

    Keep references to expensive objects without guaranteeing they stay in memory forever.

  • Resource cleanup hooks

    Track cleanup for wrapper objects that mirror underlying resources when deterministic disposal is unavailable.

Cautions

  • Garbage collection timing is intentionally non-deterministic, so weak references are not a control-flow tool.
  • Most application code should prefer explicit ownership and disposal over GC-dependent logic.

Accessibility

  • This feature does not directly change accessibility, but memory-heavy apps can benefit from better stability.
  • Never rely on finalization timing for user-visible behavior or essential state updates.

Related links