Managing events

The EventStore is a reactive in-memory event database

At its core the event store uses the Database class to store and index events

Creating an event store

import { EventStore } from "applesauce-core";

const eventStore = new EventStore();

INFO

Its recommended to only create a single event store for your app

Adding events

To add events to the event store you can use the eventStore.add method

Adding events to the event store will update any subscriptions that match that event

eventStore.timeline({kinds: [1]}).subscribe(events => {
  console.log(`timeline updated (${events.length})`)
})

const event = { kind: 1, ... }
eventStore.add(event)

Duplicate an replaceable events

The event store understands to to handle replaceable (1xxxx) and parameterized replaceable events (3xxxx)

If the event store already has the event (same id) or if its a replaceable event and it already has newer version of it. eventStore.add will returning the existing instance of the event

This allows you to easily deduplicate events from multiple relays

const incoming = [
  {
    id: "f177c37f...",
    kind: 1,
    content: "",
    pubkey: "c3ae4ad8...",
    created_at: 1733345284,
    tags: [],
    sig: "...",
  },
  {
    id: "efd33141...",
    kind: 1,
    content: "",
    pubkey: "20d29810...",
    created_at: 1733343882,
    tags: [],
    sig: "...",
  },
  // duplicate of #1
  {
    id: "f177c37f...",
    kind: 1,
    content: "",
    pubkey: "c3ae4ad8...",
    created_at: 1733345284,
    tags: [],
    sig: "...",
  },
];

const sub = eventStore.stream({ kinds: [1] }).subscribe((event) => {
  console.log("new event", event);
});

// add first event
eventStore.add(incoming[0]);

// add second event
eventStore.add(incoming[1]);

// add duplicate event
const event = eventStore.add(incoming[2]);

// since the event f177c37f has already been added
// the subscription will not update and the returned event is the original
console.log(event !== incoming[2]);

Subscribing

Subscriptions are rxjs observables that update when new events are added to the event store

Single events

Subscribing to a single event will notify you when the event has been added to the event store or when it is deleted

const event = {
  content: "Hashtags are useless.",
  created_at: 1733153425,
  id: "000021ba6f5f4da9d1f913c73dcf8fc8347052b4e74e14a2e41101c0f40792c8",
  kind: 1,
  pubkey: "3bf0c63fcb93463407af97a5e5ee64fa883d107ef9e558472c4eb9aaaefa459d",
  sig: "6f197e399d1ebae054fbc20570fc8ef113a79afaa6057125170ba81afcecea2449969c9d1dbc61ff50328cae7166e9981734ba29672d9ae45acb675ff45ebd84",
  tags: [["nonce", "8002", "16"]],
};

const sub = eventStore.event("000021ba6f5f4da9d1f913c73dcf8fc8347052b4e74e14a2e41101c0f40792c8").subscribe((event) => {
  // value maybe undefined when the event is not in the event store
  // or if it has been deleted
  if (event) {
    console.log("event has been found", event);
  }
});

eventStore.add(event);

Replaceable events

Subscribing to a replaceable event will notify you when there is a newer version or when it is deleted

const original = {
  id: "7607adc3934f368bf1a00cb1023e455707a90af94a29c2acf877dffb0ec4c0cb",
  pubkey: "d8dd41ef1e287dfc668d2473fbef8fa9deea5c2ef03947105ef568e68827e7e4",
  created_at: 1733346633,
  kind: 0,
  tags: [],
  content: '{ "name": "john" }',
  sig: "b706636043a64c5d1a07cabf66db08b1374d6efa4558e8832f5b90becb5cba190215a2ec1303e11dac494977801600b012959daa7145fba6d96ae3fcb629759e",
};

const updated = {
  id: "2f54a4491a31451cbe0d296297649af458d89df2f24d7f86d2474fd0607e29a1",
  pubkey: "d8dd41ef1e287dfc668d2473fbef8fa9deea5c2ef03947105ef568e68827e7e4",
  created_at: 1733346633,
  kind: 0,
  tags: [],
  content: '{ "name": "john smith" }',
  sig: "d66ecc0fb2b9170818defb593150563061716bce82d276d07b4b68be9ab542b2d14bb1335eb62971a84be5f315ecf32bdf53000e780a20330f63d7803a1fd95c",
};

eventStore.add(original);

// get the original and listen for any updates
const sub = eventStore
  .replaceable(0, "d8dd41ef1e287dfc668d2473fbef8fa9deea5c2ef03947105ef568e68827e7e4")
  .subscribe((event) => {
    // first event will be the original
    if (event) console.log("Profile Updated", event);
  });

// this will trigger the subscription
eventStore.add(updated);

Streams

A stream subscription takes a filter(s) and returns all events that match and notifies you when there are new events

const sub = eventStore.stream({ kinds: [1] }).subscribe((event) => {
  console.log("Found text note", event);
});

// or if you only want to subscribe to future events
const sub = eventStore.stream({ kinds: [1] }, true).subscribe((event) => {
  console.log("Found new text note", event);
});

Timelines

A timeline subscription takes a filter(s) and returns a sorted array of events that match the filter(s)

const timeline = eventStore.timeline({ kinds: [1] }).subscribe((events) => {
  console.log(events);
});

// fetch some events using another library
fetchEvents({ kinds: [1, 0] }, (event) => {
  // timeline will update for each new event
  eventStore.add(event);
});

Fallback event loaders

The event store has three optional loader methods that act as fallbacks when events are not found in the store. These loaders are particularly useful for loading user profiles or other single events on-demand when the UI needs them.

Setting up custom loaders

You can implement your own loader methods using any Nostr library or relay connection approach:

import { EventStore } from "applesauce-core";

const eventStore = new EventStore();

// Event loader - loads events by ID
eventStore.eventLoader = async (pointer) => {
  console.log("loading event", pointer);
  const event = await cache.getEventById(pointer.id);

  if (event) return event;
};

// Replaceable loader - loads kind 0, 3, 1xxxx events
eventStore.replaceableLoader = async (pointer) => {
  console.log("loading replaceable event", pointer);
  return await loadReplaceableEvent(pointer.kind, pointer.pubkey);
};

// Addressable loader - loads kind 3xxxx events
eventStore.addressableLoader = async (pointer) => {
  console.log("loading addressable event", pointer);
  const event = await fetchAddressableEvent(pointer.kind, pointer.pubkey, pointer.identifier);
  if (event) return event;
};

Now if events are subscribed to and they don't exist in the store, the loaders will be called.

const sub = eventStore
  .profile("3bf0c63fcb93463407af97a5e5ee64fa883d107ef9e558472c4eb9aaaefa459d")
  .subscribe((profile) => {
    if (profile) console.log("Profile loaded:", profile);
  });

// Console:
// loading replaceable event { kind: 0, pubkey: '3bf0c63fcb93463407af97a5e5ee64fa883d107ef9e558472c4eb9aaaefa459d' }
// Profile loaded: { name: 'fiatjaf', ... }

The loaders are called automatically and the loaded events are added to the store, making them available for future requests and updating any active subscriptions.

Using with applesauce-loaders

While you can implement loaders with any Nostr library, the applesauce-relay and applesauce-loaders packages make it much simpler:

import { EventStore } from "applesauce-core";
import { createAddressLoader, createEventLoader } from "applesauce-loaders/loaders";
import { RelayPool } from "applesauce-relay";

const eventStore = new EventStore();
const pool = new RelayPool();

// Create an address loader that handles all addressable and replaceable events
const addressLoader = createAddressLoader(pool, {
  // Try a local relay first for caching
  cacheRequest: (filters) => pool.relay("ws://localhost:4869").request(filters),
  // Fallback to public relays
  lookupRelays: ["wss://purplepag.es", "wss://relay.damus.io"],
});

// Set loaders on event store
eventStore.addressableLoader = addressLoader;
eventStore.replaceableLoader = addressLoader;

// Create an event loader that loads events by ID
const eventLoader = createEventLoader(pool, {
  // Try a local relay first for caching
  cacheRequest: (filters) => pool.relay("ws://localhost:4869").request(filters),
});

// Set loader on event store
eventStore.eventLoader = eventLoader;

Static Methods

The event store provides several methods to directly access events without creating subscriptions. These methods are useful when you need to check for or retrieve events synchronously.

Event Management

• add(event): Add a new event to the store
• remove(event): Remove an event from the store
• update(event): Notify the store that an event has been updated

Checking Event Existence

• hasEvent(id): Check if an event with a specific ID exists in the store
• hasReplaceable(kind, pubkey, identifier?): Check if a replaceable event exists for the given kind and pubkey combination

Retrieving Events

• getEvent(id): Get a single event by its ID
• getReplaceable(kind, pubkey, identifier?): Get the latest version of a replaceable event
• getReplaceableHistory(kind, pubkey, identifier?): Get the history of all versions of a replaceable event
• getByFilters(filters): Get a set of all events that match the given filter(s)
• getTimeline(filters): Get a sorted array of events that match the given filter(s)

Example usage:

// Check if an event exists
const exists = eventStore.hasEvent("000021ba6f5f...");

// Get an event by ID
const event = eventStore.getEvent("000021ba6f5f...");

// Get events matching filters
const events = eventStore.getByFilters({ kinds: [1], authors: ["000021ba6f5f..."] });

// Get a timeline of events
const timeline = eventStore.getTimeline({ kinds: [1] });

// Check and get replaceable events
const hasProfile = eventStore.hasReplaceable(0, "000021ba6f5f...");
const profile = eventStore.getReplaceable(0, "000021ba6f5f...");