Try upgrading to napi@3

Cargo.toml

@@ -13,7 +13,7 @@ crate-type = ["cdylib"]
 napi-build = "2.0"
 
 [dependencies]
-napi = { version = "2.13", features = [
+napi = { version = "3.0.0-alpha.12", features = [
 	"serde-json",
 	"napi6",
 	"tokio_rt",

src-native/data_js.rs

@@ -1,6 +1,6 @@
 use crate::data::Data;
 use anyhow::{Context, Result};
-use napi::{Env, JsUndefined};
+use napi::Env;
 
 pub fn get_data(env: &Env) -> Result<&mut Data> {
 	let data = env.get_instance_data::<Data>()?.context("No data")?;
@@ -44,8 +44,8 @@ pub fn get_paths(env: Env) -> Result<PathsJs> {
 
 #[napi(js_name = "save")]
 #[allow(dead_code)]
-pub fn save(env: Env) -> napi::Result<JsUndefined> {
+pub fn save(env: Env) -> Result<()> {
 	let data: &mut Data = get_data(&env)?;
 	data.save()?;
-	env.get_undefined()
+	Ok(())
 }

src-native/itunes_import.rs

@@ -588,19 +588,19 @@ pub struct ItunesImport {
 #[napi]
 impl ItunesImport {
 	#[napi(factory)]
-	pub fn new(env: Env) -> napi::Result<Self> {
+	pub fn new(env: Env) -> Result<Self> {
 		let data = get_data(&env)?;
 		Ok(Self {
 			new_library: Some(data.library.clone()).into(),
 			itunes_track_paths: HashMap::new().into(),
 		})
 	}
 	#[napi]
-	pub async fn start(&self, path: String, tracks_dir: String) -> napi::Result<ImportStatus> {
+	pub async fn start(&self, path: String, tracks_dir: String) -> Result<ImportStatus> {
 		Ok(import_itunes(self, path, tracks_dir).await?)
 	}
 	#[napi]
-	pub fn finish(&mut self, env: Env) -> napi::Result<()> {
+	pub fn finish(&mut self, env: Env) -> Result<()> {
 		let data = get_data(&env)?;
 		let itunes_track_paths = &mut *self.itunes_track_paths.lock().unwrap();
 		for (itunes_path, ferrum_file) in itunes_track_paths {