Struct FinalizationRegistry 

#[repr(transparent)]
pub struct FinalizationRegistry {
    pub obj: Object,
}

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

Fields

obj: Object

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 id(&self) -> u64

Get the heap ID for this value.

This is used internally for encoding values to send to JS.

pub fn unchecked_into_f64(&self) -> f64

Returns the value as f64 without type checking. Used by serde-wasm-bindgen for numeric conversions.

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

where T: JsCast,

Check if this value is an instance of a specific JS type.

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

Checked division.

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

Power operation.

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

Bitwise AND.

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

Bitwise OR.

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

Bitwise XOR.

pub fn bit_not(&self) -> JsValue

Bitwise NOT.

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

Left shift.

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

Signed right shift.

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

Unsigned right shift.

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

Add.

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

Subtract.

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

Multiply.

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

Divide.

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

Remainder.

pub fn neg(&self) -> JsValue

Negate.

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

Less than comparison.

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

Less than or equal comparison.

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

Greater than comparison.

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

Greater than or equal comparison.

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

Loose equality (==).

pub fn is_falsy(&self) -> bool

Check if this value is a falsy value in JavaScript.

pub fn is_truthy(&self) -> bool

Check if this value is a truthy value in JavaScript.

pub fn is_object(&self) -> bool

Check if this value is an object.

pub fn is_function(&self) -> bool

Check if this value is a function.

pub fn is_string(&self) -> bool

Check if this value is a string.

pub fn is_symbol(&self) -> bool

Check if this value is a symbol.

pub fn is_bigint(&self) -> bool

Check if this value is a bigint.

pub fn is_array(&self) -> bool

Check if this value is an Array.

pub fn is_undefined(&self) -> bool

Check if this value is undefined.

pub fn is_null(&self) -> bool

Check if this value is null.

pub fn is_null_or_undefined(&self) -> bool

Check if this value is null or undefined.

pub fn js_typeof(&self) -> JsValue

Get the typeof this value as a string.

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

Check if this value has a property with the given name.

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

Get the value as a bool.

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

Get the value as an f64.

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

Get the value as a string.

pub fn as_debug_string(&self) -> String

Get a debug string representation of the value.

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 BatchableResult for FinalizationRegistry

fn try_placeholder(batch: &mut Runtime) -> Option<Self>

Returns Some(placeholder) for opaque types that can be batched, None for types that require flushing to get the actual value.

impl BinaryDecode for FinalizationRegistry

fn decode(decoder: &mut DecodedData<'_>) -> Result<Self, DecodeError>

impl BinaryEncode for FinalizationRegistry

fn encode(self, encoder: &mut EncodedData)

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 EncodeTypeDef for FinalizationRegistry

fn encode_type_def(buf: &mut Vec<u8>)

Encode this type’s definition into the buffer. For primitives, this is just the TypeTag byte. For callbacks, this includes param count, param types, and return type.

impl ErasableGeneric for FinalizationRegistry

type Repr = JsValue

impl From<FinalizationRegistry> for JsValue

fn from(val: FinalizationRegistry) -> Self

Converts to this type from the input type.

impl From<FinalizationRegistry> for Object

fn from(val: FinalizationRegistry) -> Object

Converts to this type from the input type.

impl From<JsValue> for FinalizationRegistry

fn from(val: JsValue) -> Self

Converts to this type from the input type.

impl IntoJsGeneric for FinalizationRegistry

where FinalizationRegistry: JsGeneric,

type JsCanon = FinalizationRegistry

fn to_js(self) -> Self::JsCanon

impl JsCast for FinalizationRegistry

fn instanceof(__val: &JsValue) -> bool

Check if a JsValue is an instance of this type.

fn unchecked_from_js(val: JsValue) -> Self

Unchecked cast from JsValue to this type.

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

Unchecked cast from a JsValue reference to a reference of this type.

fn is_type_of(val: &JsValue) -> bool

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

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,

Try to cast this value to type T.

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

where T: JsCast,

Try to get a reference to type T from this value.

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

where T: JsCast,

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

fn unchecked_into<T>(self) -> T

where T: JsCast,

Unchecked cast to another type.

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

where T: JsCast,

Unchecked cast to a reference of another type.

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

impl Eq for FinalizationRegistry

impl StructuralPartialEq for FinalizationRegistry

impl UpcastFrom<FinalizationRegistry> for FinalizationRegistry

impl UpcastFrom<FinalizationRegistry> for JsOption<JsValue>

impl UpcastFrom<FinalizationRegistry> for JsOption<FinalizationRegistry>

impl UpcastFrom<FinalizationRegistry> for JsOption<Object>

impl UpcastFrom<FinalizationRegistry> for JsValue

impl UpcastFrom<FinalizationRegistry> for Object