Struct FinalizationRegistry 

pub struct FinalizationRegistry { /* private fields */ }

The FinalizationRegistry object lets you request a callback when an object is garbage-collected.

FinalizationRegistry provides a way to request that a cleanup callback get called at some point when an object registered with the registry has been reclaimed (garbage-collected). Cleanup callbacks are sometimes called finalizers.

Avoid where possible: cleanup callbacks should not be relied upon for anything essential. They are best used to reduce memory usage over the course of a program for objects that benefit from cleanup. Whether, when, and in what order callbacks fire is implementation-defined.

MDN documentation

Implementations

impl FinalizationRegistry

pub fn new( cleanup_callback: &Function<fn(JsValue) -> Undefined>, ) -> FinalizationRegistry

Creates a new FinalizationRegistry with the given cleanup callback.

The cleanup callback is invoked, at some point after a registered target is garbage-collected, with the held_value that was passed to FinalizationRegistry::register. Because callbacks may be deferred or skipped entirely, the callback should normally outlive the FinalizationRegistry (for example by being created via Function::from_closure).

MDN documentation

impl FinalizationRegistry

pub fn register(&self, target: &JsValue, held_value: &JsValue)

Registers target with this FinalizationRegistry. When target is reclaimed by the garbage collector the cleanup callback may be called with held_value.

target must be an object (or a non-registered symbol).

MDN documentation

impl FinalizationRegistry

pub fn register_with_token( &self, target: &JsValue, held_value: &JsValue, unregister_token: &JsValue, )

Registers target with this FinalizationRegistry, with an unregister_token that can later be passed to FinalizationRegistry::unregister to remove the registration.

target and unregister_token must be objects (or non-registered symbols), and the same value may be passed for both.

MDN documentation

impl FinalizationRegistry

pub fn unregister(&self, unregister_token: &JsValue) -> bool

Unregisters all entries registered with this FinalizationRegistry using unregister_token. Returns true if any cells were removed.

MDN documentation

Methods from Deref<Target = Object>

pub fn constructor(&self) -> Function

The constructor property returns a reference to the Object constructor function that created the instance object.

MDN documentation

pub fn has_own_property(&self, property: &JsValue) -> bool

👎Deprecated:

Use Object::hasOwn instead.

The hasOwnProperty() method returns a boolean indicating whether the object has the specified property as its own property (as opposed to inheriting it).

MDN documentation

pub fn is_prototype_of(&self, value: &JsValue) -> bool

The isPrototypeOf() method checks if an object exists in another object’s prototype chain.

MDN documentation

pub fn property_is_enumerable(&self, property: &JsValue) -> bool

The propertyIsEnumerable() method returns a Boolean indicating whether the specified property is enumerable.

MDN documentation

pub fn to_locale_string(&self) -> JsString

The toLocaleString() method returns a string representing the object. This method is meant to be overridden by derived objects for locale-specific purposes.

MDN documentation

pub fn to_string(&self) -> JsString

The toString() method returns a string representing the object.

MDN documentation

pub fn to_js_string(&self) -> JsString

The toString() method returns a string representing the object.

MDN documentation

pub fn value_of(&self) -> Object

The valueOf() method returns the primitive value of the specified object.

MDN documentation

Methods from Deref<Target = JsValue>

pub const NULL: JsValue

pub const UNDEFINED: JsValue

pub const TRUE: JsValue

pub const FALSE: JsValue

pub fn as_f64(&self) -> Option<f64>

Returns the f64 value of this JS value if it’s an instance of a number.

If this JS value is not an instance of a number then this returns None.

pub fn is_string(&self) -> bool

Tests whether this JS value is a JS string.

pub fn as_string(&self) -> Option<String>

If this JS value is a string value, this function copies the JS string value into Wasm linear memory, encoded as UTF-8, and returns it as a Rust String.

To avoid the copying and re-encoding, consider the JsString::try_from() function from js-sys instead.

If this JS value is not an instance of a string or if it’s not valid utf-8 then this returns None.

UTF-16 vs UTF-8

JavaScript strings in general are encoded as UTF-16, but Rust strings are encoded as UTF-8. This can cause the Rust string to look a bit different than the JS string sometimes. For more details see the documentation about the str type which contains a few caveats about the encodings.

pub fn as_bool(&self) -> Option<bool>

Returns the bool value of this JS value if it’s an instance of a boolean.

If this JS value is not an instance of a boolean then this returns None.

pub fn is_null(&self) -> bool

Tests whether this JS value is null

pub fn is_undefined(&self) -> bool

Tests whether this JS value is undefined

pub fn is_null_or_undefined(&self) -> bool

Tests whether this JS value is null or undefined

pub fn is_symbol(&self) -> bool

Tests whether the type of this JS value is symbol

pub fn is_object(&self) -> bool

Tests whether typeof self == "object" && self !== null.

pub fn is_array(&self) -> bool

Tests whether this JS value is an instance of Array.

pub fn is_function(&self) -> bool

Tests whether the type of this JS value is function.

pub fn is_bigint(&self) -> bool

Tests whether the type of this JS value is bigint.

pub fn js_typeof(&self) -> JsValue

Applies the unary typeof JS operator on a JsValue.

MDN documentation

pub fn js_in(&self, obj: &JsValue) -> bool

Applies the binary in JS operator on the two JsValues.

MDN documentation

pub fn is_truthy(&self) -> bool

Tests whether the value is “truthy”.

pub fn is_falsy(&self) -> bool

Tests whether the value is “falsy”.

pub fn loose_eq(&self, other: &JsValue) -> bool

Compare two JsValues for equality, using the == operator in JS.

MDN documentation

pub fn bit_not(&self) -> JsValue

Applies the unary ~ JS operator on a JsValue.

MDN documentation

pub fn unsigned_shr(&self, rhs: &JsValue) -> u32

Applies the binary >>> JS operator on the two JsValues.

MDN documentation

pub fn checked_div(&self, rhs: &JsValue) -> JsValue

Applies the binary / JS operator on two JsValues, catching and returning any RangeError thrown.

MDN documentation

pub fn pow(&self, rhs: &JsValue) -> JsValue

Applies the binary ** JS operator on the two JsValues.

MDN documentation

pub fn lt(&self, other: &JsValue) -> bool

Applies the binary < JS operator on the two JsValues.

MDN documentation

pub fn le(&self, other: &JsValue) -> bool

Applies the binary <= JS operator on the two JsValues.

MDN documentation

pub fn ge(&self, other: &JsValue) -> bool

Applies the binary >= JS operator on the two JsValues.

MDN documentation

pub fn gt(&self, other: &JsValue) -> bool

Applies the binary > JS operator on the two JsValues.

MDN documentation

pub fn unchecked_into_f64(&self) -> f64

Applies the unary + JS operator on a JsValue. Can throw.

MDN documentation

Trait Implementations

impl AsRef<FinalizationRegistry> for FinalizationRegistry

fn as_ref(&self) -> &FinalizationRegistry

Converts this type into a shared reference of the (usually inferred) input type.

impl AsRef<JsValue> for FinalizationRegistry

fn as_ref(&self) -> &JsValue

Converts this type into a shared reference of the (usually inferred) input type.

impl AsRef<Object> for FinalizationRegistry

fn as_ref(&self) -> &Object

Converts this type into a shared reference of the (usually inferred) input type.

impl Clone for FinalizationRegistry

fn clone(&self) -> FinalizationRegistry

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for FinalizationRegistry

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Deref for FinalizationRegistry

type Target = Object

The resulting type after dereferencing.

fn deref(&self) -> &Object

Dereferences the value.

impl ErasableGeneric for FinalizationRegistry

type Repr = JsValue

The singular concrete type that all generic variants can be transmuted on

impl From<FinalizationRegistry> for JsValue

fn from(obj: FinalizationRegistry) -> JsValue

Converts to this type from the input type.

impl From<FinalizationRegistry> for Object

fn from(obj: FinalizationRegistry) -> Object

Converts to this type from the input type.

impl From<JsValue> for FinalizationRegistry

fn from(obj: JsValue) -> Self

Converts to this type from the input type.

impl FromWasmAbi for FinalizationRegistry

type Abi = <JsValue as FromWasmAbi>::Abi

The Wasm ABI type that this converts from when coming back out from the ABI boundary.

unsafe fn from_abi(js: Self::Abi) -> Self

Recover a Self from Self::Abi.

impl IntoJsGeneric for FinalizationRegistry

where FinalizationRegistry: JsGeneric,

type JsCanon = FinalizationRegistry

The canonical JsGeneric form of this type.

fn to_js(self) -> FinalizationRegistry

Produce the canonical JsGeneric value for self.

impl<'a> IntoWasmAbi for &'a FinalizationRegistry

type Abi = <&'a JsValue as IntoWasmAbi>::Abi

The Wasm ABI type that this converts into when crossing the ABI boundary.

fn into_abi(self) -> Self::Abi

Convert self into Self::Abi so that it can be sent across the wasm ABI boundary.

impl IntoWasmAbi for FinalizationRegistry

type Abi = <JsValue as IntoWasmAbi>::Abi

The Wasm ABI type that this converts into when crossing the ABI boundary.

fn into_abi(self) -> Self::Abi

Convert self into Self::Abi so that it can be sent across the wasm ABI boundary.

impl JsCast for FinalizationRegistry

fn instanceof(val: &JsValue) -> bool

Performs a dynamic instanceof check to see whether the JsValue provided is an instance of this type.

fn unchecked_from_js(val: JsValue) -> Self

Performs a zero-cost unchecked conversion from a JsValue into an instance of Self

fn unchecked_from_js_ref(val: &JsValue) -> &Self

Performs a zero-cost unchecked conversion from a &JsValue into an instance of &Self.

fn has_type<T>(&self) -> bool

where T: JsCast,

Test whether this JS value has a type T.

fn dyn_into<T>(self) -> Result<T, Self>

where T: JsCast,

Performs a dynamic cast (checked at runtime) of this value into the target type T.

fn dyn_ref<T>(&self) -> Option<&T>

where T: JsCast,

Performs a dynamic cast (checked at runtime) of this value into the target type T.

fn unchecked_into<T>(self) -> T

where T: JsCast,

Performs a zero-cost unchecked cast into the specified type.

fn unchecked_ref<T>(&self) -> &T

where T: JsCast,

Performs a zero-cost unchecked cast into a reference to the specified type.

fn is_instance_of<T>(&self) -> bool

where T: JsCast,

Test whether this JS value is an instance of the type T.

fn is_type_of(val: &JsValue) -> bool

Performs a dynamic check to see whether the JsValue provided is a value of this type.

impl LongRefFromWasmAbi for FinalizationRegistry

type Abi = <JsValue as LongRefFromWasmAbi>::Abi

Same as RefFromWasmAbi::Abi

type Anchor = FinalizationRegistry

Same as RefFromWasmAbi::Anchor

unsafe fn long_ref_from_abi(js: Self::Abi) -> Self::Anchor

Same as RefFromWasmAbi::ref_from_abi

impl OptionFromWasmAbi for FinalizationRegistry

fn is_none(abi: &Self::Abi) -> bool

Tests whether the argument is a “none” instance. If so it will be deserialized as None, and otherwise it will be passed to FromWasmAbi.

impl<'a> OptionIntoWasmAbi for &'a FinalizationRegistry

fn none() -> Self::Abi

Returns an ABI instance indicating “none”, which JS will interpret as the None branch of this option.

impl OptionIntoWasmAbi for FinalizationRegistry

fn none() -> Self::Abi

Returns an ABI instance indicating “none”, which JS will interpret as the None branch of this option.

impl PartialEq for FinalizationRegistry

fn eq(&self, other: &FinalizationRegistry) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Promising for FinalizationRegistry

type Resolution = FinalizationRegistry

The type that this value resolves to.

impl RefFromWasmAbi for FinalizationRegistry

type Abi = <JsValue as RefFromWasmAbi>::Abi

The Wasm ABI type references to Self are recovered from.

type Anchor = ManuallyDrop<FinalizationRegistry>

The type that holds the reference to Self for the duration of the invocation of the function that has an &Self parameter. This is required to ensure that the lifetimes don’t persist beyond one function call, and so that they remain anonymous.

unsafe fn ref_from_abi(js: Self::Abi) -> Self::Anchor

Recover a Self::Anchor from Self::Abi.

impl WasmDescribe for FinalizationRegistry

fn describe()

impl Eq for FinalizationRegistry

impl StructuralPartialEq for FinalizationRegistry

impl UpcastFrom<FinalizationRegistry> for FinalizationRegistry

impl UpcastFrom<FinalizationRegistry> for JsOption<FinalizationRegistry>

impl UpcastFrom<FinalizationRegistry> for JsOption<Object>

impl UpcastFrom<FinalizationRegistry> for JsValue

impl UpcastFrom<FinalizationRegistry> for Object