Boxed Number Slices: Box<[u8]>, Box<[i8]>, Box<[u16]>, Box<[i16]>, Box<[u32]>, Box<[i32]>, Box<[u64]>, Box<[i64]>, Box<[f32]>, Box<[f64]>, Box<[MaybeUninit<u8>]>, Box<[MaybeUninit<i8>]>, Box<[MaybeUninit<u16>]>, Box<[MaybeUninit<i16>]>, Box<[MaybeUninit<u32>]>, Box<[MaybeUninit<i32>]>, Box<[MaybeUninit<u64>]>, Box<[MaybeUninit<i64>]>, Box<[MaybeUninit<f32>]>, and Box<[MaybeUninit<f64>]>
T parameter &T parameter &mut T parameter T return value Option<T> parameter Option<T> return value JavaScript representation
Yes No No Yes Yes Yes A JavaScript TypedArray of the appropriate type (Int32Array, Uint8Array, etc...)

Note: The contents of the slice are copied into a 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.

Note: Numeric MaybeUninit<T> can always be assumed to be initialized upon transmission from Rust to JS and vice-versa. However, uninitialized values coming from Rust might contain unspecified values.

Example Rust Usage

 

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

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

#[wasm_bindgen]
pub fn return_boxed_number_slice() -> Box<[u32]> {
    (0..42).collect::<Vec<u32>>().into_boxed_slice()
}

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

#[wasm_bindgen]
pub fn return_option_boxed_number_slice() -> Option<Box<[i32]>> {
    None
}

#}

Example JavaScript Usage

 
import {
  take_boxed_number_slice_by_value,
  return_boxed_number_slice,
  take_option_boxed_number_slice,
  return_option_boxed_number_slice,
} 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(null);
take_option_boxed_number_slice(undefined);
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
}