js准确计算字符串长度

//js准确计算字符串长度
//

function calculate_byte( sTargetStr ) {
        var sTmpStr, sTmpChar;
        var nOriginLen = 0;
        var nStrLength = 0;
        
        sTmpStr = new String(sTargetStr);
        nOriginLen = sTmpStr.length;

        for ( var i=0 ; i < nOriginLen ; i++ ) {
                sTmpChar = sTmpStr.charAt(i);

                if (escape(sTmpChar).length > 4) {
                        nStrLength += 2;
                } else if (sTmpChar!='/r') {
                        nStrLength ++;
                }
        }
       
        return nStrLength;
       
}