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title: FinalizationRegistry.prototype.unregister()
short-title: unregister()
slug: Web/JavaScript/Reference/Global_Objects/FinalizationRegistry/unregister
page-type: javascript-instance-method
browser-compat: javascript.builtins.FinalizationRegistry.unregister
sidebar: jsref
---
The **`unregister()`** method of {{jsxref("FinalizationRegistry")}} instances unregisters a target value from this `FinalizationRegistry`.
## Syntax
```js-nolint
unregister(unregisterToken)
```
### Parameters
- `unregisterToken`
- : The token used with the {{jsxref("FinalizationRegistry/register", "register()")}} method when registering the target value. Multiple cells registered with the same `unregisterToken` will 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
- {{jsxref("TypeError")}}
- : Thrown if `unregisterToken` is not an object or a [non-registered symbol](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol#shared_symbols_in_the_global_symbol_registry).
## 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`:
```js
class Thingy {
static #cleanup = (label) => {
// ^^^^^−−−−− held value
console.error(
`The "release" method was never called for the object with the label "${label}"`,
);
};
#registry = new FinalizationRegistry(Thingy.#cleanup);
/**
* Constructs a `Thingy` instance.
* Be sure to call `release` when you're done with it.
*
* @param label A label for the `Thingy`.
*/
constructor(label) {
// vvvvv−−−−− held value
this.#registry.register(this, label, this);
// target −−−−−^^^^ ^^^^−−−−− unregister token
}
/**
* Releases resources held by this `Thingy` instance.
*/
release() {
this.#registry.unregister(this);
// ^^^^−−−−− unregister token
}
}
```
This example shows registering a target object using a different object as its
unregister token:
```js
class Thingy {
static #cleanup = (file) => {
// ^^^^−−−−− held value
console.error(
`The "release" method was never called for the "Thingy" for the file "${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
{{Specifications}}
## Browser compatibility
{{Compat}}
## See also
- {{jsxref("FinalizationRegistry")}}
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