diff --git a/napi/src/env.rs b/napi/src/env.rs
index 961f5701..4b601205 100644
--- a/napi/src/env.rs
+++ b/napi/src/env.rs
@@ -1,6 +1,7 @@
 use std::any::TypeId;
 use std::convert::TryInto;
 use std::ffi::CString;
+use std::mem;
 use std::os::raw::{c_char, c_void};
 use std::ptr;
 
@@ -275,7 +276,7 @@ impl Env {
         value: raw_value,
         value_type: ValueType::Object,
       }),
-      data,
+      mem::ManuallyDrop::new(data),
     ))
   }
 
@@ -306,10 +307,55 @@ impl Env {
         value: raw_value,
         value_type: ValueType::Object,
       }),
-      data,
+      mem::ManuallyDrop::new(data),
     ))
   }
 
+  #[inline]
+  /// # Safety
+  /// Mostly same with `create_buffer_with_data`, but you must ensure data will be dropped **after** the `Buffer` is been GC.
+  ///
+  /// And should manually trigger `Env::adjust_external_memory` after data is dropped.
+  pub unsafe fn create_buffer_with_manually_drop_data(&self, data: &[u8]) -> Result<JsBufferValue> {
+    let length = data.len();
+    let mut raw_value = ptr::null_mut();
+    let data_ptr = data.as_ptr();
+    check_status!(sys::napi_create_external_buffer(
+      self.0,
+      length,
+      data_ptr as *mut c_void,
+      None,
+      ptr::null_mut(),
+      &mut raw_value,
+    ))?;
+    let mut changed = 0;
+    check_status!(sys::napi_adjust_external_memory(
+      self.0,
+      length as i64,
+      &mut changed
+    ))?;
+    Ok(JsBufferValue::new(
+      JsBuffer(Value {
+        env: self.0,
+        value: raw_value,
+        value_type: ValueType::Object,
+      }),
+      mem::ManuallyDrop::new(Vec::from_raw_parts(data_ptr as *mut u8, length, length)),
+    ))
+  }
+
+  #[inline]
+  /// This function gives V8 an indication of the amount of externally allocated memory that is kept alive by JavaScript objects (i.e. a JavaScript object that points to its own memory allocated by a native module).
+  ///
+  /// Registering externally allocated memory will trigger global garbage collections more often than it would otherwise.
+  ///
+  /// ***ATTENTION ⚠️***, do not use this with `create_buffer_with_data/create_arraybuffer_with_data`, since these two functions already called the `adjust_external_memory` internal.
+  pub fn adjust_external_memory(&mut self, size: i64) -> Result<i64> {
+    let mut changed = 0i64;
+    check_status!(unsafe { sys::napi_adjust_external_memory(self.0, size, &mut changed) })?;
+    Ok(changed)
+  }
+
   #[inline]
   /// This API allocates a node::Buffer object and initializes it with data copied from the passed-in buffer.
   /// While this is still a fully-supported data structure, in most cases using a TypedArray will suffice.
@@ -336,7 +382,7 @@ impl Env {
         value: raw_value,
         value_type: ValueType::Object,
       }),
-      unsafe { Vec::from_raw_parts(copy_data as *mut u8, length, length) },
+      mem::ManuallyDrop::new(unsafe { Vec::from_raw_parts(copy_data as *mut u8, length, length) }),
     ))
   }
 
diff --git a/napi/src/js_values/buffer.rs b/napi/src/js_values/buffer.rs
index 4cf485a8..b3926259 100644
--- a/napi/src/js_values/buffer.rs
+++ b/napi/src/js_values/buffer.rs
@@ -55,11 +55,8 @@ impl JsBufferValue {
   }
 
   #[inline]
-  pub fn new(value: JsBuffer, data: Vec<u8>) -> Self {
-    JsBufferValue {
-      value,
-      data: mem::ManuallyDrop::new(data),
-    }
+  pub fn new(value: JsBuffer, data: mem::ManuallyDrop<Vec<u8>>) -> Self {
+    JsBufferValue { value, data }
   }
 
   #[inline]
diff --git a/napi/src/js_values/mod.rs b/napi/src/js_values/mod.rs
index 326d7dd8..a2a9c76e 100644
--- a/napi/src/js_values/mod.rs
+++ b/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)
+  }
 }
diff --git a/napi/src/lib.rs b/napi/src/lib.rs
index 9230f83a..88c44844 100644
--- a/napi/src/lib.rs
+++ b/napi/src/lib.rs
@@ -6,7 +6,7 @@
 //!
 //! ## Feature flags
 //!
-//! ### napi1 ~ napi6
+//! ### napi1 ~ napi7
 //!
 //! Because `NodeJS` N-API has versions. So there are feature flags to choose what version of `N-API` you want to build for.
 //! For example, if you want build a library which can be used by `node@10.17.0`, you should choose the `napi5` or lower.
diff --git a/test_module/__test__/js-value.spec.ts b/test_module/__test__/js-value.spec.ts
index 402da262..d5bbf08c 100644
--- a/test_module/__test__/js-value.spec.ts
+++ b/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))
+})
diff --git a/test_module/src/env.rs b/test_module/src/env.rs
index 0648a4f8..43dda012 100644
--- a/test_module/src/env.rs
+++ b/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(())
 }
diff --git a/test_module/tsconfig.json b/test_module/tsconfig.json
index d1d19d67..c5cf16e7 100644
--- a/test_module/tsconfig.json
+++ b/test_module/tsconfig.json
@@ -2,7 +2,8 @@
   "extends": "../tsconfig.json",
   "include": ["."],
   "compilerOptions": {
-    "outDir": "./dist"
+    "outDir": "./dist",
+    "rootDir": "__test__"
   },
   "exclude": ["dist"]
 }