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Read a UTF8 String from a "byte" source

/ Published in: JavaScript
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This is useful if you have a string where each character represents a byte like the one returned by getStringAt() in BinaryAjax.

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  1. function readUTF8String(bytes) {
  2.     var ix = 0;
  3.  
  4.     if( bytes.slice(0,3) == "\xEF\xBB\xBF") {
  5.         ix = 3;
  6.     }
  7.  
  8.     var string = "";
  9.     for( ; ix < bytes.length; ix++ ) {
  10.         var byte1 = bytes[ix].charCodeAt(0);
  11.         if( byte1 < 0x80 ) {
  12.             string += String.fromCharCode(byte1);
  13.         } else if( byte1 >= 0xC2 && byte1 < 0xE0 ) {
  14.             var byte2 = bytes[++ix].charCodeAt(0);
  15.             string += String.fromCharCode(((byte1&0x1F)<<6) + (byte2&0x3F));
  16.         } else if( byte1 >= 0xE0 && byte1 < 0xF0 ) {
  17.             var byte2 = bytes[++ix].charCodeAt(0);
  18.             var byte3 = bytes[++ix].charCodeAt(0);
  19.             string += String.fromCharCode(((byte1&0xFF)<<12) + ((byte2&0x3F)<<6) + (byte3&0x3F));
  20.         } else if( byte1 >= 0xF0 && byte1 < 0xF5) {
  21.             var byte2 = bytes[++ix].charCodeAt(0);
  22.             var byte3 = bytes[++ix].charCodeAt(0);
  23.             var byte4 = bytes[++ix].charCodeAt(0);
  24.             var codepoint = ((byte1&0x07)<<18) + ((byte2&0x3F)<<12)+ ((byte3&0x3F)<<6) + (byte4&0x3F);
  25.             codepoint -= 0x10000;
  26.             string += String.fromCharCode(
  27.                 (codepoint>>10) + 0xD800,
  28.                 (codepoint&0x3FF) + 0xDC00
  29.             );
  30.         }
  31.     }
  32.  
  33.     return string;
  34. }

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