精确计算字符串长度【javascript】

在开发中有时要限制输入的字符数，一下函数精确计算字符串长度

其中  一个中文汉字等于两个字符

//计算字符串  
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;  
}