httpsss://js.do/powenko/04-string-length

<script>

var c="" 
function stringBytes(c){
  var n=c.length,s;
  var len=0;
  for(var i=0; i <n;i++){
   s=c.charCodeAt(i);
   while( s > 0 ){
      len++;
      s = s >> 8;
   }
  }
  return len;
}
 
var tx="測試中文12313";
console.log(stringBytes(tx));
</script>
<!-- edit your html here -->

輸出：
13