Do not mock TextDecoder

shell/cdimage.ts

@@ -1,5 +1,4 @@
 /// <reference path="util.ts" />
-/// <reference path="text-decoder.ts" />
 
 namespace CDImage {
     export class ISO9660FileSystem {
@@ -72,8 +71,7 @@ namespace CDImage {
             return this.view.getUint8(0);
         }
         volumeLabel(): string {
-            let decoder = new TextDecoder('shift_jis');
-            return decoder.decode(new DataView(this.buf, 40, 32)).trim();
+            return SJISArrayToString(new DataView(this.buf, 40, 32)).trim();
         }
         rootDirEnt(): DirEnt {
             return new DirEnt(this.buf, 156);
@@ -99,8 +97,7 @@ namespace CDImage {
         }
         get name(): string {
             let len = this.view.getUint8(32);
-            let decoder = new TextDecoder('shift_jis');
-            return decoder.decode(new DataView(this.buf, this.offset + 33, len)).split(';')[0];
+            return SJISArrayToString(new DataView(this.buf, this.offset + 33, len)).split(';')[0];
         }
     }
 
@@ -219,7 +216,7 @@ namespace CDImage {
         async parseMds(mdsFile: File) {
             let buf = await readFileAsArrayBuffer(mdsFile);
 
-            let signature = new TextDecoder().decode(new DataView(buf, 0, 16));
+            let signature = ASCIIArrayToString(new Uint8Array(buf, 0, 16));
             if (signature !== 'MEDIA DESCRIPTOR')
                 throw mdsFile.name + ': not a mds file';
 

shell/text-decoder.ts

@@ -1,18 +0,0 @@
-class FallbackTextDecoder {
-    constructor(utfLabel?: string) {}
-
-    decode(buffer: DataView): string {
-        let out = '';
-        for (let i = 0; i < buffer.byteLength; i++) {
-            let c = buffer.getUint8(i);
-            if (c < 128)
-                out += String.fromCharCode(c);
-            else
-                out += '%' + c.toString(16);
-        }
-        return out;
-    }
-}
-
-if (!(<any>window).TextDecoder)
-    (<any>window).TextDecoder = <TextEncoding.TextDecoderStatic>FallbackTextDecoder;

shell/util.ts

@@ -18,6 +18,25 @@ function readFileAsText(blob: Blob): Promise<string> {
     });
 }
 
+function ASCIIArrayToString(buffer: Uint8Array): string {
+    return String.fromCharCode.apply(null, buffer);
+}
+
+function SJISArrayToString(buffer: DataView): string {
+    if (typeof TextDecoder !== 'undefined')
+        return new TextDecoder('shift_jis').decode(buffer);
+
+    let out = '';
+    for (let i = 0; i < buffer.byteLength; i++) {
+        let c = buffer.getUint8(i);
+        if (c < 128)
+            out += String.fromCharCode(c);
+        else
+            out += '%' + c.toString(16);
+    }
+    return out;
+}
+
 declare var WebAssembly: any;
 
 // xsystem35 exported functions