docs: update example in README (#2660)

crates/napi/README.md

@@ -57,13 +57,12 @@ One nice feature is that this crate allows you to build add-ons purely with the
 ### Define JavaScript functions
 
 ```rust
-/// import the preludes
 use napi::bindgen_prelude::*;
 use napi_derive::napi;
 
 /// module registration is done by the runtime, no need to explicitly do it now.
 #[napi]
-fn fibonacci(n: u32) -> u32 {
+pub fn fibonacci(n: u32) -> u32 {
   match n {
     1 | 2 => 1,
     _ => fibonacci(n - 1) + fibonacci(n - 2),
@@ -73,30 +72,31 @@ fn fibonacci(n: u32) -> u32 {
 /// use `Fn`, `FnMut` or `FnOnce` traits to defined JavaScript callbacks
 /// the return type of callbacks can only be `Result`.
 #[napi]
-fn get_cwd<T: Fn(String) -> Result<()>>(callback: T) {
-  callback(env::current_dir().unwrap().to_string_lossy().to_string()).unwrap();
+pub fn get_cwd<T: Fn(String) -> Result<()>>(callback: T) {
+  callback(
+    std::env::current_dir()
+      .unwrap()
+      .to_string_lossy()
+      .to_string(),
+  )
+  .unwrap();
 }
 
 /// or, define the callback signature in where clause
 #[napi]
-fn test_callback<T>(callback: T)
-where T: Fn(String) -> Result<()>
-{}
+pub fn test_callback<T>(callback: T) -> Result<()>
+where
+  T: Fn(String) -> Result<()>,
+{
+  callback(std::env::current_dir()?.to_string_lossy().to_string())
+}
 
 /// async fn, require `async` feature enabled.
 /// [dependencies]
 /// napi = {version="2", features=["async"]}
 #[napi]
-async fn read_file_async(path: String) -> Result<Buffer> {
-  tokio::fs::read(path)
-    .map(|r| match r {
-      Ok(content) => Ok(content.into()),
-      Err(e) => Err(Error::new(
-        Status::GenericFailure,
-        format!("failed to read file, {}", e),
-      )),
-    })
-    .await
+pub async fn read_file_async(path: String) -> Result<Buffer> {
+  Ok(tokio::fs::read(path).await?.into())
 }
 ```