guide: Add JsValue example to supported types section

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

@@ -0,0 +1,10 @@
+import {
+  take_js_value_by_value,
+  take_js_value_by_shared_ref,
+  return_js_value,
+} from './guide_supported_types_examples';
+
+take_js_value_by_value(42);
+take_js_value_by_shared_ref('hello');
+
+let v = return_js_value();

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

@@ -0,0 +1,12 @@
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen]
+pub fn take_js_value_by_value(x: JsValue) {}
+
+#[wasm_bindgen]
+pub fn take_js_value_by_shared_ref(x: &JsValue) {}
+
+#[wasm_bindgen]
+pub fn return_js_value() -> JsValue {
+    JsValue::NULL
+}

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

@@ -9,3 +9,4 @@ pub mod str;
 pub mod string;
 pub mod char;
 pub mod bool;
+pub mod js_value;