js substr支持中文截取函数代码(中文是双字节)

<script language="JavaScript"> 
//得到字符总数
function getChars(str) {
 var i = 0;
 var c = 0.0;
 var unicode = 0;
 var len = 0;
 if (str == null || str == "") {
  return 0;
 }
 len = str.length;
 for(i = 0; i < len; i++) {
   unicode = str.charCodeAt(i);
  if (unicode < 127) { //判断是单字符还是双字符
   c += 1;
  } else {  //chinese
   c += 2;
  }
 }
 return c;
}
function sb_strlen(str) {
    return getChars(str);
}
//截取字符
function sb_substr(str, startp, endp) {
    var i=0; c = 0; unicode=0; rstr = '';
    var len = str.length;
    var sblen = sb_strlen(str);
    if (startp < 0) {
        startp = sblen + startp;
    }
    if (endp < 1) {
        endp = sblen + endp;// - ((str.charCodeAt(len-1) < 127) ? 1 : 2);
    }
    // 寻找起点
    for(i = 0; i < len; i++) {
        if (c >= startp) {
            break;
        }
     var unicode = str.charCodeAt(i);
  if (unicode < 127) {
   c += 1;
  } else {
   c += 2;
  }
 }
 // 开始取
 for(i = i; i < len; i++) {
     var unicode = str.charCodeAt(i);
  if (unicode < 127) {
   c += 1;
  } else {
   c += 2;
  }
  rstr += str.charAt(i);
  if (c >= endp) {
      break;
  }
 }
 return rstr;
}
//调用示例：
function getShortFileName(filename) {
    short_filename = filename;
    if (sb_strlen(short_filename) > 61) {
        short_filename = sb_substr(short_filename, 0, 36) + ' ... ' + sb_substr(short_filename, -20);
    }
    return short_filename;
}
var chara = 'ni你2好1啊！'
js_self = chara.substr(4);
test = sb_substr(chara,4);
alert("js_self:"+js_self+"ext:"+test);
</script>

function mb_strlen(str) {
 var len = 0;
 for(var i = 0; i < str.length; i++) {
  len += str.charCodeAt(i) < 0 || str.charCodeAt(i) > 255 ? (charset == 'utf-8' ? 3 : 2) : 1;
 }
 return len;
}

function CutStrLength(str,Ilength)
{
var tmp=0;
var len=0;
var okLen=0
for(var i=0;i255)
tmp+=2
else
len+=1
okLen+=1
if(tmp+len==Ilength)
{
return (str.substring(0,okLen));
break;
}
if(tmp+len>Ilength)
{
return (str.substring(0,okLen-1)+"");
break;
}
}
}
function checkFieldLength(fieldName,fieldDesc,fieldLength)
{
var str=document.getElementById(fieldName).value;
var theLen=0;
var teststr='';
for(i=0;i255)
theLen=theLen+2;
else
theLen=theLen+1;
}
document.getElementById('showMsg').innerText=theLen;
if(theLen>fieldLength)
{
document.getElementById('showMsg').innerText=fieldDesc;
//alert(fieldDesc+" 的字段长度超过规定长度！");
//document.getElementById(fieldName).focus();
document.getElementById(fieldName).value=CutStrLength(str,fieldLength);
return false;
}
else
{
return true;
}
}
//-->
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