var write_buffer = new Uint8Array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]);
var read_buffer = new Uint8Array(16);

var fs = new FileSystem('local');
fs.mkdir('/tmp');
fs.open('/tmp/', 'w+', function(error, fd) {
  if(error) return console.error(error);
  fs.write(fd, ...);
  fs.read(fd, ...);
});

fs.then(
  function() {
    return this.mkdir('/tmp');
  }
);

var fd = fs.open('/myfile.txt', fs.RW);

fd.then(
  function() {
    return this.write(write_buffer);
  }
).then(
  function(nbytes) {
    this.seek(-nbytes);
    return this.read(read_buffer);
  }
).then(
  function(nbytes) {
    console.log(read_buffer);
  }
);

});