计算字节长度

function getLength(str){
  var n = str.length, c, s=0;
  while(n--){
    c=str.charCodeAt(n);
    switch(true){
      case c<=0x7F: s+=1; break;
      case c<=0x7FF: s+=2; break;
      case c<=0xFFFF: s+=3; break;
      case c<=0x1FFFF: s+=4; break;
      case c<=0x7FFFFFFFF: s+=5; break;
    }
  }
  return s;
}
console.log(getLength('สวัสดี'))