[wasm] fix: NCMFile & loader issue

um_wasm/src/exports/ncm.rs

@@ -3,7 +3,7 @@ use umc_ncm::NetEaseCryptoError;
 use wasm_bindgen::prelude::wasm_bindgen;
 use wasm_bindgen::JsError;
 
-/// QMC Footer.
+/// NCMFile
 #[wasm_bindgen(js_name=NCMFile)]
 pub struct JsNCMFile {
     ncm: Option<NCMFile>,
@@ -11,6 +11,12 @@ pub struct JsNCMFile {
 
 #[wasm_bindgen(js_class=NCMFile)]
 impl JsNCMFile {
+    /// Create a NCMFile instance
+    #[wasm_bindgen(constructor)]
+    pub fn new() -> Result<JsNCMFile, JsError> {
+        Ok(JsNCMFile { ncm: None })
+    }
+
     /// Open NCM file.
     /// If everything is ok, return `0`.
     ///