examples: Add Component Locking example

Signed-off-by: Lewis Marshall <lewis.marshall@ably.com>

examples/locks.ts

@@ -0,0 +1,92 @@
+// An example of members locating at and locking elements in a slides
+// application.
+import Ably from 'ably/promises';
+import Spaces from '../dist/cjs/Spaces';
+import { Lock } from '../dist/cjs/Locks';
+
+// SlideElement represents an element on a slide which a member can both be
+// located at and attempt to lock (e.g. an editable text box).
+class SlideElement {
+  slideId: string;
+  elementId: string;
+
+  constructor(slideId: string, elementId: string) {
+    this.slideId = slideId;
+    this.elementId = elementId;
+  }
+
+  // the identifier to use to lock this SlideElement.
+  lockId(): string {
+    return `/slides/${this.slideId}/element/${this.elementId}`;
+  }
+
+  // the attributes to use when locking this SlideElement.
+  lockAttributes(): Map<string, string> {
+    const attributes = new Map();
+    attributes.set('slideId', this.slideId);
+    attributes.set('elementId', this.elementId);
+    return attributes;
+  }
+}
+
+// define a main async function since we can't use await at the top-level.
+const main = async () => {
+  info('initialising Ably client');
+  const client = new Ably.Realtime.Promise({
+    key: process.env.ABLY_API_KEY,
+    clientId: 'Alice',
+  });
+
+  info('entering the "example" space');
+  const spaces = new Spaces(client);
+  const space = await spaces.get('example');
+  await space.enter();
+
+  const location = new SlideElement('123', '456');
+  info(`setting location to ${JSON.stringify(location)}`);
+  await space.locations.set(location);
+
+  info('checking if location is locked');
+  const lockId = location.lockId();
+  const isLocked = space.locks.get(lockId) !== undefined;
+  if (isLocked) {
+    info('location is already locked');
+    process.exit();
+  } else {
+    info('location is not locked');
+  }
+
+  // initialise a Promise which resolves when the lock changes status.
+  const lockEvent = new Promise<Lock>((resolve) => {
+    const listener = (lock: Lock) => {
+      if (lock.request.id === lockId) {
+        info(`received lock update for "${lockId}", status=${lock.request.status}`);
+        resolve(lock);
+        info('unsubscribing from lock events');
+        space.locks.unsubscribe(listener);
+      }
+    };
+    info('subscribing to lock events');
+    space.locks.subscribe('update', listener);
+  });
+
+  info(`attempting to lock "${lockId}"`);
+  const req = await space.locks.acquire(lockId);
+
+  info('waiting for lock event');
+  const lock = await lockEvent;
+
+  info(`lock status is "${lock.request.status}"`);
+
+  info('releasing the lock');
+  await space.locks.release(lockId);
+
+  info('done');
+  client.close();
+};
+
+const info = (msg: string) => {
+  console.log(new Date(), 'INFO', msg);
+}
+
+main();