jsString <=> UTF8 byte array convert

utf8.js

var utf8_scope = [0x0, 0x7f, 0x7ff, 0xffff, 0x10000];
var utf8_prefix = [0x80, 0x00, 0xc0, 0xe0, 0xf0];
var utf8_valid_bits = [6, 7, 5, 4, 3];
var utf8_valid_mask = [0x3f, 0x7f, 0x1f, 0x0f, 0x07];

function str2utf(str)
{
  //if (!(str instanceof String))
    //return;

  var strbyte = new Array();

  for (var i=0; i<str.length; i++)
  {
    var unicode = str.charCodeAt(i);
    var k = 1;

    while (unicode > utf8_scope[k])
      k++;

    var utf8 = new Array();
    var j = k;
    while (j>1)
    {
      utf8.unshift(utf8_prefix[0] | (unicode & utf8_valid_mask[0]));
      unicode = unicode >> 6;
      j--;
    }
    utf8.unshift(utf8_prefix[k] | (unicode & utf8_valid_mask[k]))
    strbyte = strbyte.concat(utf8);
  }
  return(strbyte);
}

function utf2str(utf)
{
  var strbyte = new Array();
  var cbyte = 0;

  for (var i=0; i<utf.length; i++)
  {    
    var k = 0;
    while ((utf[i]&~utf8_valid_mask[k]) != utf8_prefix[k])
      k++;
    
    if (k != 0)
    {
      strbyte.push(cbyte);
      cbyte = 0;
    }

    cbyte = (cbyte << 6) | (utf[i] & utf8_valid_mask[k]);
  }
  strbyte.push(cbyte);
  strbyte.shift();
  return(String.fromCharCode.apply(null, strbyte));
}