How to count the number of bytes of a character

EDIT: Ooooops.

console.log (Buffer.byteLength ("", "utf8")); //--> 3

I want to count the number of bytes of a character. This is what I have:

var charBytesLength = function (c){
    var n = 0;
    c = c.charCodeAt (0);
    do{
        c = c >>> 8;
        n++;
    }while (c);
    return n;
};

If the character is encoded using UTF8, for characters with more than 2 bytes the function always returns 2 because in Javascript a character is a 16-bit value and charCodeAt() only returns the value between 0 and 65535.

For example:

"".charCodeAt (0)

returns 65533, when the real hexadecimal value is 0x24065 (147557 in decimal)

Do you know how to count the real number of bytes?