diff --git a/napi/src/async_work.rs b/napi/src/async_work.rs
index 231f7bfb..913ee454 100644
--- a/napi/src/async_work.rs
+++ b/napi/src/async_work.rs
@@ -39,12 +39,7 @@ pub fn run<T: Task>(env: &Env, task: T) -> Result<AsyncWorkPromise<'_>> {
   let mut raw_name = ptr::null_mut();
   let s = "napi_rs_async_work";
   check_status!(unsafe {
-    sys::napi_create_string_utf8(
-      env.0,
-      s.as_ptr() as *const c_char,
-      s.len() as _,
-      &mut raw_name,
-    )
+    sys::napi_create_string_utf8(env.0, s.as_ptr() as *const c_char, s.len(), &mut raw_name)
   })?;
   let result = Box::leak(Box::new(AsyncWork {
     inner_task: task,
diff --git a/napi/src/env.rs b/napi/src/env.rs
index 5ab7c334..d24b4be2 100644
--- a/napi/src/env.rs
+++ b/napi/src/env.rs
@@ -151,12 +151,12 @@ impl Env {
           true => 1,
           false => 0,
         },
-        len as _,
+        len,
         words.as_ptr(),
         &mut raw_value,
       )
     })?;
-    Ok(JsBigint::from_raw_unchecked(self.0, raw_value, len as _))
+    Ok(JsBigint::from_raw_unchecked(self.0, raw_value, len))
   }
 
   #[inline]
@@ -182,9 +182,7 @@ impl Env {
   #[inline]
   fn create_string_from_chars(&self, data_ptr: *const c_char, len: usize) -> Result<JsString> {
     let mut raw_value = ptr::null_mut();
-    check_status!(unsafe {
-      sys::napi_create_string_utf8(self.0, data_ptr, len as _, &mut raw_value)
-    })?;
+    check_status!(unsafe { sys::napi_create_string_utf8(self.0, data_ptr, len, &mut raw_value) })?;
     Ok(unsafe { JsString::from_raw_unchecked(self.0, raw_value) })
   }
 
@@ -192,7 +190,7 @@ impl Env {
   pub fn create_string_utf16(&self, chars: &[u16]) -> Result<JsString> {
     let mut raw_value = ptr::null_mut();
     check_status!(unsafe {
-      sys::napi_create_string_utf16(self.0, chars.as_ptr(), chars.len() as _, &mut raw_value)
+      sys::napi_create_string_utf16(self.0, chars.as_ptr(), chars.len(), &mut raw_value)
     })?;
     Ok(unsafe { JsString::from_raw_unchecked(self.0, raw_value) })
   }
@@ -204,7 +202,7 @@ impl Env {
       sys::napi_create_string_latin1(
         self.0,
         chars.as_ptr() as *const _,
-        chars.len() as _,
+        chars.len(),
         &mut raw_value,
       )
     })?;
@@ -251,9 +249,7 @@ impl Env {
   #[inline]
   pub fn create_array_with_length(&self, length: usize) -> Result<JsObject> {
     let mut raw_value = ptr::null_mut();
-    check_status!(unsafe {
-      sys::napi_create_array_with_length(self.0, length as _, &mut raw_value)
-    })?;
+    check_status!(unsafe { sys::napi_create_array_with_length(self.0, length, &mut raw_value) })?;
     Ok(unsafe { JsObject::from_raw_unchecked(self.0, raw_value) })
   }
 
@@ -264,7 +260,7 @@ impl Env {
     let mut data: Vec<u8> = Vec::with_capacity(length);
     let mut data_ptr = data.as_mut_ptr() as *mut c_void;
     check_status!(unsafe {
-      sys::napi_create_buffer(self.0, length as _, &mut data_ptr, &mut raw_value)
+      sys::napi_create_buffer(self.0, length, &mut data_ptr, &mut raw_value)
     })?;
 
     Ok(JsBufferValue::new(
@@ -287,7 +283,7 @@ impl Env {
     check_status!(unsafe {
       sys::napi_create_external_buffer(
         self.0,
-        length as _,
+        length,
         data_ptr as *mut c_void,
         Some(drop_buffer),
         &mut length as *mut usize as *mut _,
@@ -322,7 +318,7 @@ impl Env {
     check_status!(unsafe {
       sys::napi_create_buffer_copy(
         self.0,
-        length as _,
+        length,
         data_ptr as *mut c_void,
         &mut copy_data,
         &mut raw_value,
@@ -344,7 +340,7 @@ impl Env {
     let mut data: Vec<u8> = Vec::with_capacity(length as usize);
     let mut data_ptr = data.as_mut_ptr() as *mut c_void;
     check_status!(unsafe {
-      sys::napi_create_arraybuffer(self.0, length as _, &mut data_ptr, &mut raw_value)
+      sys::napi_create_arraybuffer(self.0, length, &mut data_ptr, &mut raw_value)
     })?;
 
     Ok(JsArrayBufferValue::new(
@@ -362,7 +358,7 @@ impl Env {
       sys::napi_create_external_arraybuffer(
         self.0,
         data_ptr as *mut c_void,
-        length as _,
+        length,
         Some(drop_buffer),
         &mut length as *mut usize as *mut c_void,
         &mut raw_value,
@@ -512,10 +508,10 @@ impl Env {
       sys::napi_define_class(
         self.0,
         name.as_ptr() as *const c_char,
-        name.len() as _,
+        name.len(),
         Some(constructor_cb),
         ptr::null_mut(),
-        raw_properties.len() as _,
+        raw_properties.len(),
         raw_properties.as_ptr(),
         &mut raw_result,
       )
diff --git a/napi/src/js_values/arraybuffer.rs b/napi/src/js_values/arraybuffer.rs
index 6de957f5..45b961c1 100644
--- a/napi/src/js_values/arraybuffer.rs
+++ b/napi/src/js_values/arraybuffer.rs
@@ -116,17 +116,17 @@ impl JsArrayBuffer {
   pub fn into_typedarray(
     self,
     typedarray_type: TypedArrayType,
-    length: u64,
-    byte_offset: u64,
+    length: usize,
+    byte_offset: usize,
   ) -> Result<JsTypedArray> {
     let mut typedarray_value = ptr::null_mut();
     check_status!(unsafe {
       sys::napi_create_typedarray(
         self.0.env,
         typedarray_type.into(),
-        length as _,
+        length,
         self.0.value,
-        byte_offset as _,
+        byte_offset,
         &mut typedarray_value,
       )
     })?;
@@ -138,14 +138,14 @@ impl JsArrayBuffer {
   }
 
   #[inline]
-  pub fn into_dataview(self, length: u64, byte_offset: u64) -> Result<JsDataView> {
+  pub fn into_dataview(self, length: usize, byte_offset: usize) -> Result<JsDataView> {
     let mut dataview_value = ptr::null_mut();
     check_status!(unsafe {
       sys::napi_create_dataview(
         self.0.env,
-        length as _,
+        length,
         self.0.value,
-        byte_offset as _,
+        byte_offset,
         &mut dataview_value,
       )
     })?;
diff --git a/napi/src/js_values/bigint.rs b/napi/src/js_values/bigint.rs
index 77f20895..1cfffe9a 100644
--- a/napi/src/js_values/bigint.rs
+++ b/napi/src/js_values/bigint.rs
@@ -6,7 +6,7 @@ use crate::{check_status, sys, Result};
 
 pub struct JsBigint {
   pub(crate) raw: Value,
-  pub word_count: u64,
+  pub word_count: usize,
 }
 
 impl JsBigint {
@@ -14,7 +14,7 @@ impl JsBigint {
   pub(crate) fn from_raw_unchecked(
     env: sys::napi_env,
     value: sys::napi_value,
-    word_count: u64,
+    word_count: usize,
   ) -> Self {
     Self {
       raw: Value {
@@ -128,12 +128,12 @@ impl NapiValue for JsBigint {
   }
 
   unsafe fn from_raw(env: sys::napi_env, value: sys::napi_value) -> Result<Self> {
-    let mut word_count: u64 = 0;
+    let mut word_count = 0usize;
     check_status!(sys::napi_get_value_bigint_words(
       env,
       value,
       ptr::null_mut(),
-      &mut word_count as *mut u64 as *mut _,
+      &mut word_count,
       ptr::null_mut(),
     ))?;
     Ok(JsBigint {
@@ -147,12 +147,12 @@ impl NapiValue for JsBigint {
   }
 
   unsafe fn from_raw_unchecked(env: sys::napi_env, value: sys::napi_value) -> Self {
-    let mut word_count: u64 = 0;
+    let mut word_count = 0usize;
     let status = sys::napi_get_value_bigint_words(
       env,
       value,
       ptr::null_mut(),
-      &mut word_count as *mut u64 as *mut _,
+      &mut word_count,
       ptr::null_mut(),
     );
     debug_assert!(
@@ -200,7 +200,7 @@ impl JsBigint {
         self.raw.env,
         self.raw.value,
         &mut sign_bit,
-        word_count as *mut u64 as *mut _,
+        word_count,
         words.as_mut_ptr(),
       )
     })?;
diff --git a/napi/src/js_values/function.rs b/napi/src/js_values/function.rs
index b395f395..07d5b548 100644
--- a/napi/src/js_values/function.rs
+++ b/napi/src/js_values/function.rs
@@ -43,7 +43,7 @@ impl JsFunction {
         self.0.env,
         raw_this,
         self.0.value,
-        args.len() as _,
+        args.len(),
         raw_args.as_ptr(),
         &mut return_value,
       )
@@ -70,7 +70,7 @@ impl JsFunction {
       sys::napi_new_instance(
         self.0.env,
         self.0.value,
-        length as _,
+        length,
         raw_args.as_ptr(),
         &mut js_instance,
       )
diff --git a/napi/src/js_values/mod.rs b/napi/src/js_values/mod.rs
index 56c7f386..326d7dd8 100644
--- a/napi/src/js_values/mod.rs
+++ b/napi/src/js_values/mod.rs
@@ -369,7 +369,7 @@ macro_rules! impl_object_methods {
         let mut js_key = ptr::null_mut();
         let mut result = false;
         check_status!(unsafe {
-          sys::napi_create_string_utf8(self.0.env, string.as_ptr(), name.len() as _, &mut js_key)
+          sys::napi_create_string_utf8(self.0.env, string.as_ptr(), name.len(), &mut js_key)
         })?;
         check_status!(unsafe {
           sys::napi_has_property(self.0.env, self.0.value, js_key, &mut result)
@@ -483,7 +483,7 @@ macro_rules! impl_object_methods {
           sys::napi_define_properties(
             self.0.env,
             self.0.value,
-            properties.len() as _,
+            properties.len(),
             properties
               .iter()
               .map(|property| property.raw())
diff --git a/napi/src/js_values/string/mod.rs b/napi/src/js_values/string/mod.rs
index cb2010a8..83715efa 100644
--- a/napi/src/js_values/string/mod.rs
+++ b/napi/src/js_values/string/mod.rs
@@ -55,7 +55,7 @@ impl JsString {
         self.0.env,
         self.0.value,
         buf_ptr,
-        len as _,
+        len,
         &mut written_char_count,
       )
     })?;
@@ -65,11 +65,7 @@ impl JsString {
     Ok(JsStringUtf8 {
       inner: self,
       buf: mem::ManuallyDrop::new(unsafe {
-        Vec::from_raw_parts(
-          buf_ptr as *mut _,
-          written_char_count as _,
-          written_char_count as _,
-        )
+        Vec::from_raw_parts(buf_ptr, written_char_count, written_char_count)
       }),
     })
   }
@@ -81,7 +77,7 @@ impl JsString {
 
   #[inline]
   pub fn into_utf16(self) -> Result<JsStringUtf16> {
-    let mut written_char_count = 0;
+    let mut written_char_count = 0usize;
     let len = self.utf16_len()? + 1;
     let mut result = Vec::with_capacity(len);
     let buf_ptr = result.as_mut_ptr();
@@ -90,7 +86,7 @@ impl JsString {
         self.0.env,
         self.0.value,
         buf_ptr,
-        len as _,
+        len,
         &mut written_char_count,
       )
     })?;
@@ -99,7 +95,7 @@ impl JsString {
     Ok(JsStringUtf16 {
       inner: self,
       buf: mem::ManuallyDrop::new(unsafe {
-        Vec::from_raw_parts(buf_ptr, written_char_count as _, written_char_count as _)
+        Vec::from_raw_parts(buf_ptr, written_char_count, written_char_count)
       }),
     })
   }
@@ -111,7 +107,7 @@ impl JsString {
 
   #[inline]
   pub fn into_latin1(self) -> Result<JsStringLatin1> {
-    let mut written_char_count: u64 = 0;
+    let mut written_char_count = 0usize;
     let len = self.latin1_len()? + 1;
     let mut result = Vec::with_capacity(len);
     let buf_ptr = result.as_mut_ptr();
@@ -120,8 +116,8 @@ impl JsString {
         self.0.env,
         self.0.value,
         buf_ptr,
-        len as _,
-        &mut written_char_count as *mut u64 as *mut _,
+        len,
+        &mut written_char_count,
       )
     })?;
 
@@ -130,11 +126,7 @@ impl JsString {
     Ok(JsStringLatin1 {
       inner: self,
       buf: mem::ManuallyDrop::new(unsafe {
-        Vec::from_raw_parts(
-          buf_ptr as *mut _,
-          written_char_count as _,
-          written_char_count as _,
-        )
+        Vec::from_raw_parts(buf_ptr as *mut _, written_char_count, written_char_count)
       }),
     })
   }
diff --git a/napi/src/js_values/string/utf8.rs b/napi/src/js_values/string/utf8.rs
index fb8c662d..5239b383 100644
--- a/napi/src/js_values/string/utf8.rs
+++ b/napi/src/js_values/string/utf8.rs
@@ -1,24 +1,27 @@
 use std::convert::TryFrom;
+use std::ffi::CStr;
 use std::mem::ManuallyDrop;
+use std::os::raw::c_char;
 use std::str;
 
 use crate::{Error, JsString, Result, Status};
 
 pub struct JsStringUtf8 {
   pub(crate) inner: JsString,
-  pub(crate) buf: ManuallyDrop<Vec<u8>>,
+  pub(crate) buf: ManuallyDrop<Vec<c_char>>,
 }
 
 impl JsStringUtf8 {
   #[inline]
   pub fn as_str(&self) -> Result<&str> {
-    str::from_utf8(self.buf.as_slice())
+    unsafe { CStr::from_ptr(self.buf.as_ptr()) }
+      .to_str()
       .map_err(|e| Error::new(Status::InvalidArg, format!("{}", e)))
   }
 
   #[inline]
   pub fn as_slice(&self) -> &[u8] {
-    &self.buf
+    unsafe { CStr::from_ptr(self.buf.as_ptr()) }.to_bytes()
   }
 
   #[inline]
diff --git a/napi/src/promise.rs b/napi/src/promise.rs
index a7ad507c..4ab3d4f0 100644
--- a/napi/src/promise.rs
+++ b/napi/src/promise.rs
@@ -27,7 +27,7 @@ impl<T, V: NapiValue> FuturePromise<T, V> {
       sys::napi_create_string_utf8(
         env,
         s.as_ptr() as *const c_char,
-        s.len() as _,
+        s.len(),
         &mut async_resource_name,
       )
     })?;
@@ -55,7 +55,7 @@ impl<T, V: NapiValue> FuturePromise<T, V> {
         ptr::null_mut(),
         async_resource_name,
         0,
-        initial_thread_count as _,
+        initial_thread_count,
         ptr::null_mut(),
         None,
         self_ref as *mut _ as *mut c_void,
diff --git a/napi/src/threadsafe_function.rs b/napi/src/threadsafe_function.rs
index cb94e88d..82d581ba 100644
--- a/napi/src/threadsafe_function.rs
+++ b/napi/src/threadsafe_function.rs
@@ -1,6 +1,7 @@
 use std::convert::Into;
+use std::ffi::CString;
 use std::marker::PhantomData;
-use std::os::raw::{c_char, c_void};
+use std::os::raw::c_void;
 use std::ptr;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
@@ -104,16 +105,13 @@ impl<T: 'static> ThreadsafeFunction<T> {
   ) -> Result<Self> {
     let mut async_resource_name = ptr::null_mut();
     let s = "napi_rs_threadsafe_function";
+    let len = s.len();
+    let s = CString::new(s)?;
     check_status!(unsafe {
-      sys::napi_create_string_utf8(
-        env,
-        s.as_ptr() as *const c_char,
-        s.len() as _,
-        &mut async_resource_name,
-      )
+      sys::napi_create_string_utf8(env, s.as_ptr(), len, &mut async_resource_name)
     })?;
 
-    let initial_thread_count = 1;
+    let initial_thread_count = 1usize;
     let mut raw_tsfn = ptr::null_mut();
     let context = ThreadSafeContext(Box::from(callback));
     let ptr = Box::into_raw(Box::new(context)) as *mut _;
@@ -123,7 +121,7 @@ impl<T: 'static> ThreadsafeFunction<T> {
         func.0.value,
         ptr::null_mut(),
         async_resource_name,
-        max_queue_size as _,
+        max_queue_size,
         initial_thread_count,
         ptr,
         Some(thread_finalize_cb::<T, V>),
@@ -280,7 +278,7 @@ unsafe extern "C" fn call_js_cb<T: 'static, V: NapiValue>(
         raw_env,
         recv,
         js_callback,
-        args_length as _,
+        args_length,
         args.as_ptr(),
         ptr::null_mut(),
       );