FileLoader: Support environments without ReadableStream (#23032)

src/loaders/FileLoader.js

@@ -84,6 +84,12 @@ class FileLoader extends Loader {
 
 					}
 
+					if ( typeof ReadableStream === 'undefined' || response.body.getReader === undefined ) {
+
+						return response;
+
+					}
+
 					const callbacks = loading[ url ];
 					const reader = response.body.getReader();
 					const contentLength = response.headers.get( 'Content-Length' );
@@ -92,7 +98,7 @@ class FileLoader extends Loader {
 					let loaded = 0;
 
 					// periodically read data into the new stream tracking while download progress
-					return new ReadableStream( {
+					const stream = new ReadableStream( {
 						start( controller ) {
 
 							readData();
@@ -130,16 +136,16 @@ class FileLoader extends Loader {
 
 					} );
 
+					return new Response( stream );
+
 				} else {
 
 					throw Error( `fetch for "${response.url}" responded with ${response.status}: ${response.statusText}` );
 
 				}
 
 			} )
-			.then( stream => {
-
-				const response = new Response( stream );
+			.then( response => {
 
 				switch ( this.responseType ) {