Struct JsBox

pub struct JsBox<T: 'static>(/* private fields */);

A JavaScript smart pointer object that owns Rust data.

The type JsBox<T> provides shared ownership of a value of type T, allocated in the heap. The data is owned by the JavaScript engine and the lifetime is managed by the JavaScript garbage collector.

Shared references in Rust disallow mutation by default, and JsBox is no exception: you cannot generally obtain a mutable reference to something inside a JsBox. If you need to mutate through a JsBox, use Cell, RefCell, or one of the other types that provide interior mutability.

Values contained by a JsBox must implement the Finalize trait. Finalize::finalize will execute with the value in a JsBox immediately before the JsBox is garbage collected. If no additional finalization is necessary, an emply implementation may be provided.

Deref behavior

JsBox<T> automatically dereferences to T (via the Deref trait), so you can call T’s method on a value of type JsBox<T>.

let vec: Handle<JsBox<Vec<_>>> = cx.boxed(vec![1, 2, 3]);

println!("Length: {}", vec.len());

Examples

Passing some immutable data between Rust and JavaScript.

fn create_path(mut cx: FunctionContext) -> JsResult<JsBox<PathBuf>> {
    let path = cx.argument::<JsString>(0)?.value(&mut cx);
    let path = Path::new(&path).to_path_buf();

    Ok(cx.boxed(path))
}

fn print_path(mut cx: FunctionContext) -> JsResult<JsUndefined> {
    let path = cx.argument::<JsBox<PathBuf>>(0)?;

    println!("{}", path.display());

    Ok(cx.undefined())
}

Passing a user defined struct wrapped in a RefCell for mutability. This pattern is useful for creating classes in JavaScript.

type BoxedPerson = JsBox<RefCell<Person>>;

struct Person {
     name: String,
}

impl Finalize for Person {}

impl Person {
    pub fn new(name: String) -> Self {
        Person { name }
    }

    pub fn set_name(&mut self, name: String) {
        self.name = name;
    }

    pub fn greet(&self) -> String {
        format!("Hello, {}!", self.name)
    }
}

fn person_new(mut cx: FunctionContext) -> JsResult<BoxedPerson> {
    let name = cx.argument::<JsString>(0)?.value(&mut cx);
    let person = RefCell::new(Person::new(name));

    Ok(cx.boxed(person))
}

fn person_set_name(mut cx: FunctionContext) -> JsResult<JsUndefined> {
    let person = cx.argument::<BoxedPerson>(0)?;
    let mut person = person.borrow_mut();
    let name = cx.argument::<JsString>(1)?.value(&mut cx);

    person.set_name(name);

    Ok(cx.undefined())
}

fn person_greet(mut cx: FunctionContext) -> JsResult<JsString> {
    let person = cx.argument::<BoxedPerson>(0)?;
    let person = person.borrow();
    let greeting = person.greet();

    Ok(cx.string(greeting))
}

Implementations

impl<T: Finalize + 'static> JsBox<T>

Values contained by a JsBox must be Finalize + 'static

Finalize

The sys::prelude::Finalize trait provides a finalize method that will be called immediately before the JsBox is garbage collected.

`‘static’

The lifetime of a JsBox is managed by the JavaScript garbage collector. Since Rust is unable to verify the lifetime of the contents, references must be valid for the entire duration of the program. This does not mean that the JsBox will be valid until the application terminates, only that its lifetime is indefinite.

pub fn new<'a, C>(cx: &mut C, value: T) -> Handle<'a, JsBox<T>>

where C: Context<'a>, T: 'static,

Constructs a new JsBox containing value.

impl<T: 'static> JsBox<T>

pub fn deref<'cx>(v: &Handle<'cx, Self>) -> &'cx T

Gets a reference to the inner value of a JsBox. This method is similar to dereferencing a JsBox (e.g., &*boxed), but the lifetime is safely extended to 'cx.

See also Handle<JsBox>::as_inner.

Trait Implementations

impl<T: 'static> Debug for JsBox<T>

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

Formats the value using the given formatter.

impl<T: 'static> Deref for JsBox<T>

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl<T: 'static> Object for JsBox<T>

fn prop<'a, 'cx: 'a, K: PropertyKey>( &self, cx: &'a mut Cx<'cx>, key: K, ) -> PropOptions<'a, 'cx, Self, K>

Create a PropOptions for accessing a property.

fn method<'a, 'cx: 'a, K: PropertyKey>( &self, cx: &'a mut Cx<'cx>, key: K, ) -> NeonResult<BindOptions<'a, 'cx>>

Gets a property from the object as a method and binds this to the object.

fn get_opt<'a, V: Value, C: Context<'a>, K: PropertyKey>( &self, cx: &mut C, key: K, ) -> NeonResult<Option<Handle<'a, V>>>

👎Deprecating in a future version: use Object::prop() instead

fn get_value<'a, C: Context<'a>, K: PropertyKey>( &self, cx: &mut C, key: K, ) -> NeonResult<Handle<'a, JsValue>>

👎Deprecating in a future version: use Object::prop() instead

fn get<'a, V: Value, C: Context<'a>, K: PropertyKey>( &self, cx: &mut C, key: K, ) -> NeonResult<Handle<'a, V>>

👎Deprecating in a future version: use Object::prop() instead

fn get_own_property_names<'a, C: Context<'a>>( &self, cx: &mut C, ) -> JsResult<'a, JsArray>

Available on crate feature napi-6 only.

fn freeze<'a, C: Context<'a>>(&self, cx: &mut C) -> NeonResult<&Self>

fn seal<'a, C: Context<'a>>(&self, cx: &mut C) -> NeonResult<&Self>

fn set<'a, C: Context<'a>, K: PropertyKey, W: Value>( &self, cx: &mut C, key: K, val: Handle<'_, W>, ) -> NeonResult<bool>

👎Deprecating in a future version: use Object::prop() instead

fn root<'a, C: Context<'a>>(&self, cx: &mut C) -> Root<Self>

fn call_method_with<'a, C, K>( &self, cx: &mut C, method: K, ) -> NeonResult<CallOptions<'a>>

where C: Context<'a>, K: PropertyKey,

👎Deprecating in a future version: use Object::method() instead

impl<T: 'static> Value for JsBox<T>

fn to_string<'cx, C: Context<'cx>>(&self, cx: &mut C) -> JsResult<'cx, JsString>

fn as_value<'cx, C: Context<'cx>>(&self, _: &mut C) -> Handle<'cx, JsValue>

fn to_raw(&self) -> Value

Available on crate feature sys only.

Get a raw reference to the wrapped Node-API value.

unsafe fn from_raw<'cx, C: Context<'cx>>( cx: &C, value: Value, ) -> Handle<'cx, Self>

Available on crate feature sys only.

Creates a value from a raw Node-API value.