added enable decoding to StringBuilder

src/core/pdf417/decoder/DecodedBitStreamParser.ts

@@ -128,10 +128,18 @@ export default /*final*/ class DecodedBitStreamParser {
    * @throws FormatException
    */
   static decode(codewords: Int32Array, ecLevel: string): DecoderResult {
+    // pass encoding to result (will be used for decode symbols in byte mode)
+    let result: StringBuilder = new StringBuilder('');
     // let encoding: Charset = StandardCharsets.ISO_8859_1;
     let encoding = CharacterSetECI.ISO8859_1;
-    // pass encoding to result (will be used for decode symbols in byte mode)
-    let result: StringBuilder = new StringBuilder('', encoding);
+    /**
+     * @note the next command is specific from this TypeScript library
+     * because TS can't properly cast some values to char and
+     * convert it to string later correctlt due to encoding
+     * differences from Java version. As reported here:
+     * https://github.com/zxing-js/library/pull/264/files#r382831593
+     */
+    result.enableDecoding(encoding);
     // Get compaction mode
     let codeIndex: int = 1;
     let code: int = codewords[codeIndex++];

src/core/util/StringBuilder.ts

@@ -1,16 +1,26 @@
+import CharacterSetECI from '../common/CharacterSetECI';
 import StringEncoding from './StringEncoding';
 
+
 export default class StringBuilder {
 
-  public constructor(private value: string = '', private format = null) {}
+  private encoding: CharacterSetECI;
+
+  public constructor(private value: string = '') {}
+
+  public enableDecoding(encoding: CharacterSetECI): StringBuilder {
+    this.encoding = encoding
+    return this;
+  }
 
   public append(s: string | number): StringBuilder {
     if (typeof s === 'string') {
       this.value += s.toString();
-    } else if (this.format) {
+    } else if (this.encoding) {
       // use passed format (fromCharCode will return UTF8 encoding)
-      this.value += StringEncoding.decode(new Uint8Array([s]), this.format);
+      this.value += StringEncoding.decode(new Uint8Array([s]), this.encoding);
     } else {
+      // correctly converts from UTF-8, but not other encodings
       this.value += String.fromCharCode(s);
     }
     return this;