Struct neon::types::JsFunction

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pub struct JsFunction { /* private fields */ }
Expand description

The type of JavaScript Function objects.

A JsFunction may come from an existing JavaScript function, for example by extracting it from the property of another object such as the global object, or it may be defined in Rust with JsFunction::new().

§Calling functions

Neon provides a convenient syntax for calling JavaScript functions with the call_with() method, which produces a CallOptions struct that can be used to provide the function arguments (and optionally, the binding for this) before calling the function:

// Extract the parseInt function from the global object
let parse_int: Handle<JsFunction> = cx.global("parseInt")?;

// Call parseInt("42")
let x: Handle<JsNumber> = parse_int
    .call_with(&mut cx)
    .arg(cx.string("42"))
    .apply(&mut cx)?;

§Calling functions as constructors

A JsFunction can be called as a constructor (like new Array(16) or new URL("https://neon-bindings.com")) with the construct_with() method:

// Extract the URL constructor from the global object
let url: Handle<JsFunction> = cx.global("URL")?;

// Call new URL("https://neon-bindings.com")
let obj = url
    .construct_with(&cx)
    .arg(cx.string("https://neon-bindings.com"))
    .apply(&mut cx)?;

§Defining functions

JavaScript functions can be defined in Rust with the JsFunction::new() constructor, which takes a Rust implementation function and produces a JavaScript function.

// A function implementation that adds 1 to its first argument
fn add1(mut cx: FunctionContext) -> JsResult<JsNumber> {
    let x: Handle<JsNumber> = cx.argument(0)?;
    let v = x.value(&mut cx);
    Ok(cx.number(v + 1.0))
}

// Define a new JsFunction implemented with the add1 function
let f = JsFunction::new(&mut cx, add1)?;

Implementations§

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impl JsFunction

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pub fn new<'a, C, F, V>(cx: &mut C, f: F) -> JsResult<'a, JsFunction>
where C: Context<'a>, F: Fn(FunctionContext<'_>) -> JsResult<'_, V> + 'static, V: Value,

Returns a new JsFunction implemented by f.

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impl JsFunction

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pub fn call<'a, 'b, C: Context<'a>, T, AS>( &self, cx: &mut C, this: Handle<'b, T>, args: AS ) -> JsResult<'a, JsValue>
where T: Value, AS: AsRef<[Handle<'b, JsValue>]>,

Calls this function.

See also: JsFunction::call_with.

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pub fn exec<'a, 'b, C: Context<'a>, T, AS>( &self, cx: &mut C, this: Handle<'b, T>, args: AS ) -> NeonResult<()>
where T: Value, AS: AsRef<[Handle<'b, JsValue>]>,

Calls this function for side effect, discarding its result.

See also: JsFunction::call_with.

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pub fn construct<'a, 'b, C: Context<'a>, AS>( &self, cx: &mut C, args: AS ) -> JsResult<'a, JsObject>
where AS: AsRef<[Handle<'b, JsValue>]>,

Calls this function as a constructor.

See also: JsFunction::construct_with.

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impl JsFunction

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pub fn call_with<'a, C: Context<'a>>(&self, _cx: &C) -> CallOptions<'a>

Create a CallOptions for calling this function.

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pub fn construct_with<'a, C: Context<'a>>( &self, _cx: &C ) -> ConstructOptions<'a>

Create a ConstructOptions for calling this function as a constructor.

Trait Implementations§

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impl Debug for JsFunction

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

Formats the value using the given formatter. Read more
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impl Object for JsFunction

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

Gets a property from a JavaScript object that may be undefined and attempts to downcast the value if it existed.
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fn get_value<'a, C: Context<'a>, K: PropertyKey>( &self, cx: &mut C, key: K ) -> NeonResult<Handle<'a, JsValue>>

Gets a property from a JavaScript object as a JsValue. Read more
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fn get<'a, V: Value, C: Context<'a>, K: PropertyKey>( &self, cx: &mut C, key: K ) -> NeonResult<Handle<'a, V>>

Gets a property from a JavaScript object and attempts to downcast as a specific type. Equivalent to calling obj.get_value(&mut cx)?.downcast_or_throw(&mut cx). Read more
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fn get_own_property_names<'a, C: Context<'a>>( &self, cx: &mut C ) -> JsResult<'a, JsArray>

Available on crate feature napi-6 only.
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fn freeze<'a, C: Context<'a>>(&self, cx: &mut C) -> NeonResult<&Self>

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

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

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

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

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impl Value for JsFunction

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

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

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fn to_raw(&self) -> Value

Available on crate feature sys only.
Get a raw reference to the wrapped Node-API value.
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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. Read more

Auto Trait Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.