feat(napi): unsafe cast JsUnknown to the other JsValue

napi/src/js_values/mod.rs

@@ -607,4 +607,15 @@ impl JsUnknown {
   pub fn get_type(&self) -> Result<ValueType> {
     unsafe { type_of!(self.0.env, self.0.value) }
   }
+
+  #[inline]
+  /// # Safety
+  /// This function should be called after `JsUnknown::get_type`
+  /// And the `V` must be match with the return value of `get_type`
+  pub unsafe fn cast<V>(self) -> V
+  where
+    V: NapiValue,
+  {
+    V::from_raw_unchecked(self.0.env, self.0.value)
+  }
 }

test_module/__test__/js-value.spec.ts

@@ -47,3 +47,14 @@ test('strict_equals', (t) => {
   t.false(bindings.strictEquals(NaN, NaN))
   t.true(bindings.strictEquals(a, a))
 })
+
+test('cast_unknown', (t) => {
+  const f = {}
+  const r = bindings.castUnknown(f)
+  t.is(f, r)
+})
+
+test('cast_unknown will not throw', (t) => {
+  const f = 1
+  t.notThrows(() => bindings.castUnknown(f))
+})

test_module/src/env.rs

@@ -26,10 +26,17 @@ pub fn strict_equals(ctx: CallContext) -> Result<JsBoolean> {
   ctx.env.get_boolean(ctx.env.strict_equals(a, b)?)
 }
 
+#[js_function(1)]
+pub fn cast_unknown(ctx: CallContext) -> Result<JsObject> {
+  let arg: JsUnknown = ctx.get(0)?;
+  Ok(unsafe { arg.cast::<JsObject>() })
+}
+
 pub fn register_js(exports: &mut JsObject) -> Result<()> {
   exports.create_named_method("instanceof", instanceof)?;
   exports.create_named_method("isTypedarray", is_typedarray)?;
   exports.create_named_method("isDataview", is_dataview)?;
   exports.create_named_method("strictEquals", strict_equals)?;
+  exports.create_named_method("castUnknown", cast_unknown)?;
   Ok(())
 }