guide: Add Box<[JsValue]> example to supported types section

examples/guide-supported-types-examples/boxed_js_value_slice.js

@@ -0,0 +1,22 @@
+import {
+  take_boxed_js_value_slice_by_value,
+  return_boxed_js_value_slice,
+  take_option_boxed_js_value_slice,
+  return_option_boxed_js_value_slice,
+} from './guide_supported_types_examples';
+
+take_boxed_js_value_slice_by_value([null, true, 2, {}, []]);
+
+let values = return_boxed_js_value_slice();
+console.log(values instanceof Array); // true
+
+take_option_boxed_js_value_slice(null);
+take_option_boxed_js_value_slice(undefined);
+take_option_boxed_js_value_slice([1, 2, 3]);
+
+let maybeValues = return_option_boxed_js_value_slice();
+if (maybeValues == null) {
+  // ...
+} else {
+  console.log(maybeValues instanceof Array); // true
+}

examples/guide-supported-types-examples/src/boxed_js_value_slice.rs

@@ -0,0 +1,17 @@
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen]
+pub fn take_boxed_js_value_slice_by_value(x: Box<[JsValue]>) {}
+
+#[wasm_bindgen]
+pub fn return_boxed_js_value_slice() -> Box<[JsValue]> {
+    vec![JsValue::NULL, JsValue::UNDEFINED].into_boxed_slice()
+}
+
+#[wasm_bindgen]
+pub fn take_option_boxed_js_value_slice(x: Option<Box<[JsValue]>>) {}
+
+#[wasm_bindgen]
+pub fn return_option_boxed_js_value_slice() -> Option<Box<[JsValue]>> {
+    None
+}

examples/guide-supported-types-examples/src/lib.rs

@@ -10,3 +10,4 @@ pub mod string;
 pub mod char;
 pub mod bool;
 pub mod js_value;
+pub mod boxed_js_value_slice;

guide/src/reference/types.md

@@ -145,6 +145,18 @@ garbage-collected heap and the Wasm linear memory with `TextDecoder` and
 |:---:|:---:|:---:|:---:|:---:|:---:|:---:|
 | Yes | No | No | Yes | Yes | Yes | A JavaScript `Array` object |
 
+### Example Rust Usage
+
+```rust
+{{#include ../../../examples/guide-supported-types-examples/src/boxed_js_value_slice.rs}}
+```
+
+### Example JavaScript Usage
+
+```js
+{{#include ../../../examples/guide-supported-types-examples/boxed_js_value_slice.js}}
+```
+
 ## `*const T` `*mut T`
 
 | `T` parameter | `&T` parameter | `&mut T` parameter | `T` return value | `Option<T>` parameter | `Option<T>` return value | JavaScript representation |