夜的第七章

function GetByteOfNum(val, num)
{
  var ch,bytenum=0;
  var rs = "";
  var pt = /[^\x00-\xff]/;
  for (var i=0; i < num; i++)
  {
   ch = val.substr(i, 1);
   if (ch.match(pt))
   {
    bytenum += 2;
    if (bytenum > num)
    {
     return rs;
    }
   }else
   {
    bytenum += 1;
   }
   rs += ch;
   if (bytenum == num)
   {
    return rs;
   }
  }
  return rs;
 }


function MaxLength(v,len)
{   
    var ascLen = v.value.replace(/[^\x00-\xff]/g,"**").length;
    
    if(ascLen > len)
    {   
        v.value = GetByteOfNum(v.value,len);
    }   
}