add type declaration

js/fetch_types.d.ts

@@ -30,6 +30,7 @@ type ReferrerPolicy =
   | "origin-when-cross-origin"
   | "unsafe-url";
 type BlobPart = BufferSource | Blob | string;
+type FormDataEntryValue = File | string;
 declare type EventListenerOrEventListenerObject =
   | EventListener
   | EventListenerObject;
@@ -42,10 +43,6 @@ interface HTMLFormElement {
   // TODO
 }
 
-interface FormDataEntryValue {
-  // TODO
-}
-
 interface BlobPropertyBag {
   type?: string;
 }
@@ -141,6 +138,20 @@ interface Event {
   readonly NONE: number;
 }
 
+interface File extends Blob {
+  readonly lastModified: number;
+  readonly name: string;
+}
+
+declare var File: {
+  prototype: File;
+  new(fileBits: BlobPart[], fileName: string, options?: FilePropertyBag): File;
+};
+
+interface FilePropertyBag extends BlobPropertyBag {
+  lastModified?: number;
+}
+
 interface ProgressEvent extends Event {
   readonly lengthComputable: boolean;
   readonly loaded: number;