ser-list.js

function serializeList(items) {
  var size = 0;
  var i, p, data;

  for (i = 0; i < items.length; i++)
    size += 4 + items[i].length;

  data = new Buffer(size);
  p = 0;

  for (i = 0; i < items.length; i++) {
    data.writeUInt32LE(items[i].length, p); // ideally a varint
    p += 4;
    data.write(items[i], p, 'ascii');
    p += items[i].length;
  }

  return data;
}

function parseItem(data, index) {
  var p = 0;
  var i = 0;
  var len;

  // Skip over every item until we
  // find the one we're looking for.
  while (p < data.length) {
    len = data.readUInt32LE(p);
    p += 4;

    // Found the item.
    if (i === index)
      return data.toString('ascii', p, p + len);

    // Not ours, skip to the next item.
    p += len;
    i++;
  }

  // Not found.
  return null;
}

function putList(items, callback) {
  db.put('list', serializeList(items), callback);
}

function getItem(index, callback) {
  db.get('list', function(err, data) {
    if (err)
      return callback(err);

    return callback(null, parseItem(data, index));
  });
}

var items = [
  'large string0',
  'large string1',
  'large string2'
];

putList(items, function(err) {
  if (err)
    throw err;
  getItem(1, function(err, item) {
    if (err)
      throw err;
    console.log(item); // large string 1
  });
});