FinalizationRegistry.prototype.unregister()
Baseline
Widely available
*
This feature is well established and works across many devices and browser versions. It’s been available across browsers since April 2021.
* Some parts of this feature may have varying levels of support.
The unregister() method of FinalizationRegistry instances unregisters a target value from this FinalizationRegistry.
Syntax
unregister(unregisterToken)
Parameters
unregisterToken-
The token used with the
register()method when registering the target value. Multiple cells registered with the sameunregisterTokenwill be unregistered together.
Return value
A boolean value that is true if at least one cell was unregistered and false if no cell was unregistered.
Exceptions
TypeError-
Thrown if
unregisterTokenis not an object or a non-registered symbol.
Description
When a target value has been reclaimed, it is no longer registered in the registry.
There is no need to call unregister in your cleanup callback. Only call
unregister if you haven't received a cleanup callback and no longer need
to receive one.
Examples
Using unregister
This example shows registering a target object using that same object as the unregister
token, then later unregistering it via unregister:
class Thingy {
static #cleanup = (label) => {
// ^^^^^−−−−− held value
console.error(
`The "release" method was never called for the object with the label "${label}"`,
);
};
#registry = new FinalizationRegistry(Thingy.#cleanup);
/**
* Constructs a `Thingy` instance.
* Be sure to call `release` when you're done with it.
*
* @param label A label for the `Thingy`.
*/
constructor(label) {
// vvvvv−−−−− held value
this.#registry.register(this, label, this);
// target −−−−−^^^^ ^^^^−−−−− unregister token
}
/**
* Releases resources held by this `Thingy` instance.
*/
release() {
this.#registry.unregister(this);
// ^^^^−−−−− unregister token
}
}
This example shows registering a target object using a different object as its unregister token:
class Thingy {
static #cleanup = (file) => {
// ^^^^−−−−− held value
console.error(
`The "release" method was never called for the "Thingy" for the file "${file.name}"`,
);
};
#registry = new FinalizationRegistry(Thingy.#cleanup);
#file;
/**
* Constructs a `Thingy` instance for the given file.
* Be sure to call `release` when you're done with it.
*
* @param filename The name of the file.
*/
constructor(filename) {
this.#file = File.open(filename);
// vvvvv−−−−− held value
this.#registry.register(this, label, this.#file);
// target −−−−−^^^^ ^^^^^^^^^^−−−−− unregister token
}
/**
* Releases resources held by this `Thingy` instance.
*/
release() {
if (this.#file) {
this.#registry.unregister(this.#file);
// ^^^^^^^^^^−−−−− unregister token
File.close(this.#file);
this.#file = null;
}
}
}
Specifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-finalization-registry.prototype.unregister |