The mock socket

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The mock socket

modules/mock-socket is a serverless stand-in for a live WebSocket feed, for building and demonstrating a real-time UI with no backend. MockWebSocket presents the same surface as the browser's WebSocket - the same readyState and state constants, the same onopen, onmessage, onclose and onerror, addEventListener, send and close - so the code that reads it does not change when it is swapped for a real one. It fires an initial snapshot the moment it opens, then a stream of deltas on a timer, all from a generator you hand it. It is a dev and test utility: optional, imports nothing from the grid, and is never pulled into the core bundle. It pairs naturally with the data router (one mock stream, partitioned to many grids), but depends on it no more than a real socket does.

import { MockWebSocket, opsFeed } from '@toclocoinc/lattice-grid/modules/mock-socket';

const socket = new MockWebSocket({ feed: opsFeed({ seed: 7 }) });
socket.onmessage = (event) => {
  const message = JSON.parse(event.data);
  if (message.kind === 'snapshot') router.load(message.rows);
  else router.apply(message.changes);
};

// Going live is the one line that changes; everything above stays as written:
const socket = new WebSocket('wss://example.com/ops');

The swap is literally one line. Both sockets frame their messages the same way, so the reader parses event.data and switches on kind either way. The feed is seedable and deterministic: the shipped generators carry their own seed and the timing jitter is seeded too, so the same inputs replay the same stream - which is what lets a tutorial and its runnable example show the same thing every time, and what lets a test assert on an exact stream rather than a plausible one. Bring your own generator: a feed is any iterator that yields { kind: 'snapshot', rows } first and then { kind: 'delta', changes } forever - a plain generator function is the easiest form - and rng(seed) is exported so a custom feed can be seeded the same way the shipped ones are.

Type reference

Generated from the type declarations, so it always matches the release. Each surface lists its properties, its methods and the events it raises as three tables; an option or value type lists its members once.

The mock socket

FeedMessage