function find_byte(buffer, b) {
    let i;
    for(i = 0; i < buffer.length; i++) {
        if(buffer[i] === b) {
            return i;
        }
    }
    return -1;
}

const buffer = Buffer.from('ascii A is byte value sixty-five', 'utf8');
const r = find_byte(buffer, 65);
console.log(r);