Bug 1590022 - Use union return value for FileReader.result, r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D49876

--HG--
extra : moz-landing-system : lando

dom/file/FileReader.cpp

@@ -143,31 +143,25 @@ FileReader::GetInterface(const nsIID& aIID, void** aResult) {
   return QueryInterface(aIID, aResult);
 }
 
-void FileReader::GetResult(JSContext* aCx, JS::MutableHandle<JS::Value> aResult,
-                           ErrorResult& aRv) {
+void FileReader::GetResult(JSContext* aCx,
+                           Nullable<OwningStringOrArrayBuffer>& aResult) {
   JS::Rooted<JS::Value> result(aCx);
 
   if (mDataFormat == FILE_AS_ARRAYBUFFER) {
-    if (mReadyState == DONE && mResultArrayBuffer) {
-      result.setObject(*mResultArrayBuffer);
-    } else {
-      result.setNull();
+    if (mReadyState != DONE || !mResultArrayBuffer ||
+        !aResult.SetValue().SetAsArrayBuffer().Init(mResultArrayBuffer)) {
+      aResult.SetNull();
     }
 
-    if (!JS_WrapValue(aCx, &result)) {
-      aRv.Throw(NS_ERROR_FAILURE);
-      return;
-    }
-
-    aResult.set(result);
     return;
   }
 
-  nsString tmpResult = mResult;
-  if (!xpc::StringToJsval(aCx, tmpResult, aResult)) {
-    aRv.Throw(NS_ERROR_FAILURE);
+  if (mResult.IsVoid()) {
+    aResult.SetNull();
     return;
   }
+
+  aResult.SetValue().SetAsString() = mResult;
 }
 
 void FileReader::OnLoadEndArrayBuffer() {

dom/file/FileReader.h

@@ -27,6 +27,7 @@ namespace dom {
 
 class Blob;
 class DOMException;
+class OwningStringOrArrayBuffer;
 class StrongWorkerRef;
 class WeakWorkerRef;
 
@@ -93,8 +94,7 @@ class FileReader final : public DOMEventTargetHelper,
 
   DOMException* GetError() const { return mError; }
 
-  void GetResult(JSContext* aCx, JS::MutableHandle<JS::Value> aResult,
-                 ErrorResult& aRv);
+  void GetResult(JSContext* aCx, Nullable<OwningStringOrArrayBuffer>& aResult);
 
   IMPL_EVENT_HANDLER(loadstart)
   IMPL_EVENT_HANDLER(progress)

dom/webidl/FileReader.webidl

@@ -34,10 +34,7 @@ interface FileReader : EventTarget {
 
   readonly attribute unsigned short readyState;
 
-  // File or Blob data
-  // bug 858217: readonly attribute (DOMString or ArrayBuffer)? result;
-  [Throws]
-  readonly attribute any result;
+  readonly attribute (DOMString or ArrayBuffer)? result;
 
   readonly attribute DOMException? error;