diff --git a/napi/src/env.rs b/napi/src/env.rs
index e8f14862..8311dc78 100644
--- a/napi/src/env.rs
+++ b/napi/src/env.rs
@@ -16,6 +16,8 @@ use crate::{sys, Error, NodeVersion, Result, Status};
 use crate::js_values::{De, Ser};
 #[cfg(all(any(feature = "libuv", feature = "tokio_rt"), napi4))]
 use crate::promise;
+#[cfg(napi4)]
+use crate::threadsafe_function::{ThreadSafeCallContext, ThreadsafeFunction};
 #[cfg(all(feature = "tokio_rt", napi4))]
 use crate::tokio_rt::{get_tokio_sender, Message};
 #[cfg(all(feature = "libuv", napi4))]
@@ -554,6 +556,20 @@ impl Env {
     })
   }
 
+  #[cfg(napi4)]
+  pub fn create_threadsafe_function<
+    T: Send,
+    V: NapiValue,
+    R: 'static + Send + FnMut(ThreadSafeCallContext<T>) -> Result<Vec<V>>,
+  >(
+    &self,
+    func: JsFunction,
+    max_queue_size: u64,
+    callback: R,
+  ) -> Result<ThreadsafeFunction<T>> {
+    ThreadsafeFunction::create(self.0, func, max_queue_size, callback)
+  }
+
   #[cfg(all(feature = "libuv", napi4))]
   pub fn execute<
     T: 'static + Send,
diff --git a/napi/src/promise.rs b/napi/src/promise.rs
index 0ea2abb7..34fa4a65 100644
--- a/napi/src/promise.rs
+++ b/napi/src/promise.rs
@@ -71,8 +71,6 @@ pub(crate) struct TSFNValue(sys::napi_threadsafe_function);
 
 unsafe impl Send for TSFNValue {}
 
-unsafe impl Sync for TSFNValue {}
-
 #[inline]
 pub(crate) async fn resolve_from_future<T: Send, F: Future<Output = Result<T>>>(
   tsfn_value: TSFNValue,
diff --git a/napi/src/threadsafe_function.rs b/napi/src/threadsafe_function.rs
index 5dd3f741..7be56e1b 100644
--- a/napi/src/threadsafe_function.rs
+++ b/napi/src/threadsafe_function.rs
@@ -1,13 +1,19 @@
 use std::convert::Into;
+use std::marker::PhantomData;
 use std::os::raw::{c_char, c_void};
 use std::ptr;
 
 use crate::error::check_status;
-use crate::{sys, Env, JsFunction, JsUnknown, Result};
+use crate::{sys, Env, JsFunction, NapiValue, Result};
 
 use sys::napi_threadsafe_function_call_mode;
 use sys::napi_threadsafe_function_release_mode;
 
+pub struct ThreadSafeCallContext<T: 'static> {
+  pub env: Env,
+  pub value: T,
+}
+
 #[repr(u8)]
 pub enum ThreadsafeFunctionCallMode {
   NonBlocking,
@@ -46,12 +52,6 @@ impl Into<napi_threadsafe_function_release_mode> for ThreadsafeFunctionReleaseMo
   }
 }
 
-pub trait ToJs: Copy + Clone {
-  type Output;
-
-  fn resolve(&self, env: &mut Env, output: Self::Output) -> Result<Vec<JsUnknown>>;
-}
-
 /// Communicate with the addon's main thread by invoking a JavaScript function from other threads.
 ///
 /// ## Example
@@ -62,71 +62,71 @@ pub trait ToJs: Copy + Clone {
 /// extern crate napi_derive;
 ///
 /// use std::thread;
+///
 /// use napi::{
-///   Number, Result, Env, CallContext, JsUndefined, JsFunction,
+///   threadsafe_function::{
+///     ThreadSafeCallContext, ThreadsafeFunctionCallMode, ThreadsafeFunctionReleaseMode,
+///   },
+///   CallContext, Error, JsFunction, JsNumber, JsUndefined, Result, Status,
 /// };
-/// use napi::threadsafe_function::{
-///   ToJs, ThreadsafeFunction, ThreadsafeFunctionCallMode, ThreadsafeFunctionReleaseMode,
-/// };
-///
-/// // Define a struct for handling the data passed from `ThreadsafeFunction::call`
-/// // and return the data to be used for the js callback.
-/// #[derive(Clone, Copy)]
-/// struct HandleNumber;
-///
-/// impl ToJs for HandleNumber {
-///   type Output = u8;
-///
-///   fn resolve(&self, env: &mut Env, output: Self::Output) -> Result<Vec<JsUnknown>> {
-///     let value = env.create_uint32(output as u32)?.into_unknown()?;
-///     // The first argument in the NodeJS callback will be either a null or an error
-///     // depending on the result returned by this function.
-///     // If this Result is Ok, the first argument will be null.
-///     // If this Result is Err, the first argument will be the error.
-///     Ok(vec![value])
-///   }
-/// }
-///
+
 /// #[js_function(1)]
-/// fn test_threadsafe_function(ctx: CallContext) -> Result<JsUndefined> {
-///   // The callback function from js which will be called in `ThreadsafeFunction::call`.
+/// pub fn test_threadsafe_function(ctx: CallContext) -> Result<JsUndefined> {
 ///   let func = ctx.get::<JsFunction>(0)?;
-///
-///   let to_js = HandleNumber;
-///   let tsfn = ThreadsafeFunction::create(ctx.env, func, to_js, 0)?;
-///
+
+///   let tsfn =
+///     ctx
+///       .env
+///       .create_threadsafe_function(func, 0, |ctx: ThreadSafeCallContext<Vec<u32>>| {
+///         ctx
+///           .value
+///           .iter()
+///           .map(|v| ctx.env.create_uint32(*v))
+///           .collect::<Result<Vec<JsNumber>>>()
+///       })?;
+
 ///   thread::spawn(move || {
-///     let output: u8 = 42;
-///     // It's okay to call a threadsafe function multiple times.
-///     tsfn.call(Ok(output), ThreadsafeFunctionCallMode::Blocking).unwrap();
-///     tsfn.call(Ok(output), ThreadsafeFunctionCallMode::Blocking).unwrap();
-///     // We should call `ThreadsafeFunction::release` manually when we don't
-///     // need the instance anymore, or it will prevent Node.js from exiting
-///     // automatically and possibly cause memory leaks.
-///     tsfn.release(ThreadsafeFunctionReleaseMode::Release).unwrap();
+///     let output: Vec<u32> = vec![42, 1, 2, 3];
+///     /// It's okay to call a threadsafe function multiple times.
+///     tsfn.call(Ok(output.clone()), ThreadsafeFunctionCallMode::Blocking);
+///     tsfn.call(Ok(output.clone()), ThreadsafeFunctionCallMode::NonBlocking);
+///     tsfn.release(ThreadsafeFunctionReleaseMode::Release);
 ///   });
-///
+
 ///   ctx.env.get_undefined()
 /// }
 /// ```
-#[derive(Debug, Clone, Copy)]
-pub struct ThreadsafeFunction<T: ToJs> {
-  raw_value: sys::napi_threadsafe_function,
-  to_js: T,
+pub struct ThreadsafeFunction<T: 'static> {
+  raw_tsfn: sys::napi_threadsafe_function,
+  _phantom: PhantomData<T>,
 }
 
-unsafe impl<T: ToJs> Send for ThreadsafeFunction<T> {}
-unsafe impl<T: ToJs> Sync for ThreadsafeFunction<T> {}
+unsafe impl<T> Send for ThreadsafeFunction<T> {}
+unsafe impl<T> Sync for ThreadsafeFunction<T> {}
 
-impl<T: ToJs> ThreadsafeFunction<T> {
+#[repr(transparent)]
+struct ThreadSafeContext<T: 'static, V: NapiValue>(
+  Box<dyn FnMut(ThreadSafeCallContext<T>) -> Result<Vec<V>>>,
+);
+
+impl<T: 'static> ThreadsafeFunction<T> {
   /// See [napi_create_threadsafe_function](https://nodejs.org/api/n-api.html#n_api_napi_create_threadsafe_function)
   /// for more information.
-  pub fn create(env: &Env, func: JsFunction, to_js: T, max_queue_size: u64) -> Result<Self> {
+  #[inline(always)]
+  pub fn create<
+    V: NapiValue,
+    R: 'static + Send + FnMut(ThreadSafeCallContext<T>) -> Result<Vec<V>>,
+  >(
+    env: sys::napi_env,
+    func: JsFunction,
+    max_queue_size: u64,
+    callback: R,
+  ) -> Result<Self> {
     let mut async_resource_name = ptr::null_mut();
     let s = "napi_rs_threadsafe_function";
     check_status(unsafe {
       sys::napi_create_string_utf8(
-        env.0,
+        env,
         s.as_ptr() as *const c_char,
         s.len() as u64,
         &mut async_resource_name,
@@ -134,59 +134,65 @@ impl<T: ToJs> ThreadsafeFunction<T> {
     })?;
 
     let initial_thread_count: u64 = 1;
-    let mut result = ptr::null_mut();
-    let tsfn = ThreadsafeFunction {
-      to_js,
-      raw_value: result,
-    };
-
-    let ptr = Box::into_raw(Box::from(tsfn)) as *mut _ as *mut c_void;
-
-    let status = unsafe {
+    let mut raw_tsfn = ptr::null_mut();
+    let context = ThreadSafeContext(Box::from(callback));
+    let ptr = Box::into_raw(Box::new(context)) as *mut _;
+    check_status(unsafe {
       sys::napi_create_threadsafe_function(
-        env.0,
+        env,
         func.0.value,
         ptr::null_mut(),
         async_resource_name,
         max_queue_size,
         initial_thread_count,
         ptr,
-        Some(thread_finalize_cb::<T>),
+        Some(thread_finalize_cb::<T, V>),
         ptr,
-        Some(call_js_cb::<T>),
-        &mut result,
+        Some(call_js_cb::<T, V>),
+        &mut raw_tsfn,
       )
-    };
-    check_status(status)?;
+    })?;
 
     Ok(ThreadsafeFunction {
-      to_js,
-      raw_value: result,
+      raw_tsfn,
+      _phantom: PhantomData,
     })
   }
 
   /// See [napi_call_threadsafe_function](https://nodejs.org/api/n-api.html#n_api_napi_call_threadsafe_function)
   /// for more information.
-  pub fn call(&self, value: Result<T::Output>, mode: ThreadsafeFunctionCallMode) -> Result<()> {
-    check_status(unsafe {
+  pub fn call(&self, value: Result<T>, mode: ThreadsafeFunctionCallMode) {
+    let status = unsafe {
       sys::napi_call_threadsafe_function(
-        self.raw_value,
-        Box::into_raw(Box::from(value)) as *mut _ as *mut c_void,
+        self.raw_tsfn,
+        Box::into_raw(Box::new(value)) as *mut _,
         mode.into(),
       )
-    })
+    };
+    debug_assert!(
+      status == sys::napi_status::napi_ok,
+      "Threadsafe Function call failed"
+    );
   }
 
   /// See [napi_acquire_threadsafe_function](https://nodejs.org/api/n-api.html#n_api_napi_acquire_threadsafe_function)
   /// for more information.
-  pub fn acquire(&self) -> Result<()> {
-    check_status(unsafe { sys::napi_acquire_threadsafe_function(self.raw_value) })
+  pub fn acquire(&self) {
+    let status = unsafe { sys::napi_acquire_threadsafe_function(self.raw_tsfn) };
+    debug_assert!(
+      status == sys::napi_status::napi_ok,
+      "Threadsafe Function acquire failed"
+    );
   }
 
   /// See [napi_release_threadsafe_function](https://nodejs.org/api/n-api.html#n_api_napi_release_threadsafe_function)
   /// for more information.
-  pub fn release(&self, mode: ThreadsafeFunctionReleaseMode) -> Result<()> {
-    check_status(unsafe { sys::napi_release_threadsafe_function(self.raw_value, mode.into()) })
+  pub fn release(self, mode: ThreadsafeFunctionReleaseMode) {
+    let status = unsafe { sys::napi_release_threadsafe_function(self.raw_tsfn, mode.into()) };
+    debug_assert!(
+      status == sys::napi_status::napi_ok,
+      "Threadsafe Function call failed"
+    );
   }
 
   /// See [napi_ref_threadsafe_function](https://nodejs.org/api/n-api.html#n_api_napi_ref_threadsafe_function)
@@ -194,73 +200,76 @@ impl<T: ToJs> ThreadsafeFunction<T> {
   ///
   /// "ref" is a keyword so that we use "refer" here.
   pub fn refer(&self, env: &Env) -> Result<()> {
-    check_status(unsafe { sys::napi_ref_threadsafe_function(env.0, self.raw_value) })
+    check_status(unsafe { sys::napi_ref_threadsafe_function(env.0, self.raw_tsfn) })
   }
 
   /// See [napi_unref_threadsafe_function](https://nodejs.org/api/n-api.html#n_api_napi_unref_threadsafe_function)
   /// for more information.
   pub fn unref(&self, env: &Env) -> Result<()> {
-    check_status(unsafe { sys::napi_unref_threadsafe_function(env.0, self.raw_value) })
+    check_status(unsafe { sys::napi_unref_threadsafe_function(env.0, self.raw_tsfn) })
   }
 }
 
-unsafe extern "C" fn thread_finalize_cb<T: ToJs>(
+unsafe extern "C" fn thread_finalize_cb<T: 'static, V: NapiValue>(
   _raw_env: sys::napi_env,
   finalize_data: *mut c_void,
   _finalize_hint: *mut c_void,
 ) {
   // cleanup
-  Box::from_raw(finalize_data as *mut ThreadsafeFunction<T>);
+  Box::from_raw(finalize_data as *mut ThreadSafeContext<T, V>);
 }
 
-unsafe extern "C" fn call_js_cb<T: ToJs>(
+unsafe extern "C" fn call_js_cb<T: 'static, V: NapiValue>(
   raw_env: sys::napi_env,
   js_callback: sys::napi_value,
   context: *mut c_void,
   data: *mut c_void,
 ) {
-  let mut env = Env::from_raw(raw_env);
   let mut recv = ptr::null_mut();
   sys::napi_get_undefined(raw_env, &mut recv);
 
-  let tsfn = Box::leak(Box::from_raw(context as *mut ThreadsafeFunction<T>));
-  let val = Box::from_raw(data as *mut Result<T::Output>);
+  let ctx = Box::leak(Box::from_raw(context as *mut ThreadSafeContext<T, V>));
+  let val = Box::from_raw(data as *mut Result<T>);
 
-  let ret = val.and_then(|v| tsfn.to_js.resolve(&mut env, v));
+  let ret = val.and_then(|v| {
+    (ctx.0)(ThreadSafeCallContext {
+      env: Env::from_raw(raw_env),
+      value: v,
+    })
+  });
 
   let status;
 
   // Follow async callback conventions: https://nodejs.org/en/knowledge/errors/what-are-the-error-conventions/
   // Check if the Result is okay, if so, pass a null as the first (error) argument automatically.
   // If the Result is an error, pass that as the first argument.
-  if ret.is_ok() {
-    let values = ret.unwrap();
-    let js_null = env.get_null().unwrap();
-    let mut raw_values: Vec<sys::napi_value> = vec![];
-    raw_values.push(js_null.0.value);
-    for item in values.iter() {
-      raw_values.push(item.0.value)
+  match ret {
+    Ok(values) => {
+      let mut js_null = ptr::null_mut();
+      sys::napi_get_null(raw_env, &mut js_null);
+      let args_length = values.len() + 1;
+      let mut args: Vec<sys::napi_value> = Vec::with_capacity(args_length);
+      args.push(js_null);
+      args.extend(values.iter().map(|v| v.raw()));
+      status = sys::napi_call_function(
+        raw_env,
+        recv,
+        js_callback,
+        args_length as _,
+        args.as_ptr(),
+        ptr::null_mut(),
+      );
+    }
+    Err(e) => {
+      status = sys::napi_call_function(
+        raw_env,
+        recv,
+        js_callback,
+        1,
+        [e.into_raw(raw_env)].as_mut_ptr(),
+        ptr::null_mut(),
+      );
     }
-
-    status = sys::napi_call_function(
-      raw_env,
-      recv,
-      js_callback,
-      (values.len() + 1) as u64,
-      raw_values.as_ptr(),
-      ptr::null_mut(),
-    );
-  } else {
-    let mut err = env.create_error(ret.err().unwrap()).unwrap();
-    status = sys::napi_call_function(
-      raw_env,
-      recv,
-      js_callback,
-      1,
-      &mut err.0.value,
-      ptr::null_mut(),
-    );
   }
-
   debug_assert!(status == sys::napi_status::napi_ok, "CallJsCB failed");
 }
diff --git a/test_module/src/napi4/mod.rs b/test_module/src/napi4/mod.rs
index 52296cae..fd78fc40 100644
--- a/test_module/src/napi4/mod.rs
+++ b/test_module/src/napi4/mod.rs
@@ -5,8 +5,8 @@ mod tsfn;
 use tsfn::*;
 
 pub fn register_js(module: &mut Module) -> Result<()> {
-  module.create_named_method("testTsfnError", test_tsfn_error)?;
   module.create_named_method("testThreadsafeFunction", test_threadsafe_function)?;
+  module.create_named_method("testTsfnError", test_tsfn_error)?;
   module.create_named_method("testTokioReadfile", test_tokio_readfile)?;
   Ok(())
 }
diff --git a/test_module/src/napi4/tsfn.rs b/test_module/src/napi4/tsfn.rs
index 214363c9..a4a01608 100644
--- a/test_module/src/napi4/tsfn.rs
+++ b/test_module/src/napi4/tsfn.rs
@@ -1,47 +1,35 @@
 use std::path::Path;
 use std::thread;
 
-use napi::threadsafe_function::{
-  ThreadsafeFunction, ThreadsafeFunctionCallMode, ThreadsafeFunctionReleaseMode, ToJs,
+use napi::{
+  threadsafe_function::{
+    ThreadSafeCallContext, ThreadsafeFunctionCallMode, ThreadsafeFunctionReleaseMode,
+  },
+  CallContext, Error, JsFunction, JsNumber, JsString, JsUndefined, Result, Status,
 };
-use napi::{CallContext, Env, Error, JsFunction, JsString, JsUndefined, JsUnknown, Result, Status};
 use tokio;
 
-#[derive(Clone, Copy)]
-struct HandleNumber;
-
-impl ToJs for HandleNumber {
-  type Output = Vec<u8>;
-
-  fn resolve(&self, env: &mut Env, output: Self::Output) -> Result<Vec<JsUnknown>> {
-    let mut items: Vec<JsUnknown> = vec![];
-    for item in output.iter() {
-      let value = env.create_uint32((*item) as u32)?.into_unknown();
-      items.push(value);
-    }
-    Ok(items)
-  }
-}
-
 #[js_function(1)]
 pub fn test_threadsafe_function(ctx: CallContext) -> Result<JsUndefined> {
   let func = ctx.get::<JsFunction>(0)?;
 
-  let to_js = HandleNumber;
-  let tsfn = ThreadsafeFunction::create(ctx.env, func, to_js, 0)?;
+  let tsfn =
+    ctx
+      .env
+      .create_threadsafe_function(func, 0, |ctx: ThreadSafeCallContext<Vec<u32>>| {
+        ctx
+          .value
+          .iter()
+          .map(|v| ctx.env.create_uint32(*v))
+          .collect::<Result<Vec<JsNumber>>>()
+      })?;
 
   thread::spawn(move || {
-    let output: Vec<u8> = vec![42, 1, 2, 3];
+    let output: Vec<u32> = vec![42, 1, 2, 3];
     // It's okay to call a threadsafe function multiple times.
-    tsfn
-      .call(Ok(output.clone()), ThreadsafeFunctionCallMode::Blocking)
-      .unwrap();
-    tsfn
-      .call(Ok(output.clone()), ThreadsafeFunctionCallMode::Blocking)
-      .unwrap();
-    tsfn
-      .release(ThreadsafeFunctionReleaseMode::Release)
-      .unwrap();
+    tsfn.call(Ok(output.clone()), ThreadsafeFunctionCallMode::Blocking);
+    tsfn.call(Ok(output.clone()), ThreadsafeFunctionCallMode::NonBlocking);
+    tsfn.release(ThreadsafeFunctionReleaseMode::Release);
   });
 
   ctx.env.get_undefined()
@@ -50,36 +38,22 @@ pub fn test_threadsafe_function(ctx: CallContext) -> Result<JsUndefined> {
 #[js_function(1)]
 pub fn test_tsfn_error(ctx: CallContext) -> Result<JsUndefined> {
   let func = ctx.get::<JsFunction>(0)?;
-  let to_js = HandleNumber;
-  let tsfn = ThreadsafeFunction::create(ctx.env, func, to_js, 0)?;
-
+  let tsfn = ctx
+    .env
+    .create_threadsafe_function(func, 0, |ctx: ThreadSafeCallContext<()>| {
+      ctx.env.get_undefined().map(|v| vec![v])
+    })?;
   thread::spawn(move || {
-    tsfn
-      .call(
-        Err(Error::new(Status::Unknown, "invalid".to_owned())),
-        ThreadsafeFunctionCallMode::Blocking,
-      )
-      .unwrap();
-    tsfn
-      .release(ThreadsafeFunctionReleaseMode::Release)
-      .unwrap();
+    tsfn.call(
+      Err(Error::new(Status::Unknown, "invalid".to_owned())),
+      ThreadsafeFunctionCallMode::Blocking,
+    );
+    tsfn.release(ThreadsafeFunctionReleaseMode::Release);
   });
 
   ctx.env.get_undefined()
 }
 
-#[derive(Copy, Clone)]
-struct HandleBuffer;
-
-impl ToJs for HandleBuffer {
-  type Output = Vec<u8>;
-
-  fn resolve(&self, env: &mut Env, output: Self::Output) -> Result<Vec<JsUnknown>> {
-    let value = env.create_buffer_with_data(output.to_vec())?.into_unknown();
-    Ok(vec![value])
-  }
-}
-
 async fn read_file_content(filepath: &Path) -> Result<Vec<u8>> {
   tokio::fs::read(filepath)
     .await
@@ -92,16 +66,22 @@ pub fn test_tokio_readfile(ctx: CallContext) -> Result<JsUndefined> {
   let js_func = ctx.get::<JsFunction>(1)?;
   let path_str = js_filepath.into_utf8()?.to_owned()?;
 
-  let to_js = HandleBuffer;
-  let tsfn = ThreadsafeFunction::create(ctx.env, js_func, to_js, 0)?;
-  let mut rt = tokio::runtime::Runtime::new().unwrap();
+  let tsfn =
+    ctx
+      .env
+      .create_threadsafe_function(js_func, 0, |ctx: ThreadSafeCallContext<Vec<u8>>| {
+        ctx
+          .env
+          .create_buffer_with_data(ctx.value)
+          .map(|v| vec![v.into_raw()])
+      })?;
+  let mut rt = tokio::runtime::Runtime::new()
+    .map_err(|e| Error::from_reason(format!("Create tokio runtime failed {}", e)))?;
 
   rt.block_on(async move {
     let ret = read_file_content(&Path::new(&path_str)).await;
-    let _ = tsfn.call(ret, ThreadsafeFunctionCallMode::Blocking);
-    tsfn
-      .release(ThreadsafeFunctionReleaseMode::Release)
-      .unwrap();
+    tsfn.call(ret, ThreadsafeFunctionCallMode::Blocking);
+    tsfn.release(ThreadsafeFunctionReleaseMode::Release);
   });
 
   ctx.env.get_undefined()