Struct neon::types::JsFunction

#[repr(C)]
pub struct JsFunction<T: Object = JsObject> { /* fields omitted */ }

A JavaScript function object.

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> = global
    .get(&mut cx, "parseInt")?
    .downcast_or_throw(&mut cx)?;

// 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> = global
    .get(&mut cx, "URL")?
    .downcast_or_throw(&mut cx)?;

// 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

impl JsFunction

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

impl<CL: Object> JsFunction<CL>

pub fn call<'a, 'b, C: Context<'a>, T, A, AS>(
    self,
    cx: &mut C,
    this: Handle<'b, T>,
    args: AS
) -> JsResult<'a, JsValue> where
    T: Value,
    A: Value + 'b,
    AS: IntoIterator<Item = Handle<'b, A>>, 

pub fn construct<'a, 'b, C: Context<'a>, A, AS>(
    self,
    cx: &mut C,
    args: AS
) -> JsResult<'a, CL> where
    A: Value + 'b,
    AS: IntoIterator<Item = Handle<'b, A>>, 

impl JsFunction

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

Create a CallOptions for calling this function.

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

impl<T: Clone + Object> Clone for JsFunction<T>

fn clone(&self) -> JsFunction<T>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<T: Object> Managed for JsFunction<T>

fn to_raw(self) -> Local

fn from_raw(_: Env, h: Local) -> Self

impl<T: Object> Object for JsFunction<T>

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

This is supported on crate feature napi-1 only.

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

This is supported on crate features napi-1 and napi-6 only.

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

This is supported on crate feature napi-1 only.

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

This is supported on crate feature napi-1 only.

impl<T: Object> Value for JsFunction<T>

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

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

impl<T: Copy + Object> Copy for JsFunction<T>