FileLoader: `text` honors mimetype's charset as encoding (#23292)

* honor encoding

* npm run lint-fix

* cmp idx

* lint

* textual encoding

* record state

* new api `.setResponseType`

* rollback mmdloader

* sniff encoding for 'text' kind

src/loaders/FileLoader.js

@@ -69,6 +69,10 @@ class FileLoader extends Loader {
 			// An abort controller could be added within a future PR
 		} );
 
+		// record states ( avoid data race )
+		const mimeType = this.mimeType;
+		const responseType = this.responseType;
+
 		// start the fetch
 		fetch( req )
 			.then( response => {
@@ -147,7 +151,7 @@ class FileLoader extends Loader {
 			} )
 			.then( response => {
 
-				switch ( this.responseType ) {
+				switch ( responseType ) {
 
 					case 'arraybuffer':
 
@@ -163,7 +167,7 @@ class FileLoader extends Loader {
 							.then( text => {
 
 								const parser = new DOMParser();
-								return parser.parseFromString( text, this.mimeType );
+								return parser.parseFromString( text, mimeType );
 
 							} );
 
@@ -173,7 +177,20 @@ class FileLoader extends Loader {
 
 					default:
 
-						return response.text();
+						if ( mimeType === undefined ) {
+
+							return response.text();
+
+						} else {
+
+							// sniff encoding
+							const re = /charset="?([^;"\s]*)"?/i;
+							const exec = re.exec( mimeType );
+							const label = exec && exec[ 1 ] ? exec[ 1 ].toLowerCase() : undefined;
+							const decoder = new TextDecoder( label );
+							return response.arrayBuffer().then( ab => decoder.decode( ab ) );
+
+						}
 
 				}