https://js.do/powenko/04-string-length
[php]

<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 –>

[/php]
輸出：
13