This is the unpublished documentation of wasm-bindgen, the published documentation is available on the main Rust and WebAssembly documentation site . Features documented here may not be available in released versions of wasm-bindgen.

Boxed Number Slices: Box<[u8]>, Box<[i8]>, Box<[u16]>, Box<[i16]>, Box<[u32]>, Box<[i32]>, Box<[u64]>, Box<[i64]>, Box<[f32]>, and Box<[f64]>

T parameter&T parameter&mut T parameterT return valueOption<T> parameterOption<T> return valueJavaScript representation
YesNoNoYesYesYesA JavaScript TypedArray of the appropriate type (Int32Array, Uint8Array, etc...)

Note that the contents of the slice are copied into the JavaScript TypedArray from the Wasm linear memory when returning a boxed slice to JavaScript, and vice versa when receiving a JavaScript TypedArray as a boxed slice in Rust.

Example Rust Usage

# #![allow(unused_variables)]
#fn main() {
use wasm_bindgen::prelude::*;

pub fn take_boxed_number_slice_by_value(x: Box<[f64]>) {}

pub fn return_boxed_number_slice() -> Box<[u32]> {

pub fn take_option_boxed_number_slice(x: Option<Box<[u8]>>) {}

pub fn return_option_boxed_number_slice() -> Option<Box<[i32]>> {


Example JavaScript Usage

import {
} from './guide_supported_types_examples';

take_boxed_number_slice_by_value(new Uint8Array(100));

let x = return_boxed_number_slice();
console.log(x instanceof Uint32Array); // true

take_option_boxed_number_slice(new Int16Array(256));

let y = return_option_boxed_number_slice();
if (y == null) {
  // ...
} else {
  console.log(x instanceof Int32Array); // true