学步园

function   coder(str)   
  {   
 
        var   s   =   "";   
        if   (str.length   ==   0)   return   "";   
        for   (var   i=0;   i<str.length;   i++)   
        {   
              switch   (str.substr(i,1))   
              {   
                      case   "<"     :   s   +=   "<";       break;   
                      case   ">"     :   s   +=   ">";       break;   
                      case   "&"     :   s   +=   "&";     break;   
                      case   "   "     :   s   +=   " ";   break;   
                      case   "\""   :   s   +=   """;   break;   
                      case   "\n"   :   s   +=   "<br>";       break;   
                      default       :   s   +=   str.substr(i,1);   break;   
              }   
        }   
        return   s;   
  }