[DTP-963] Add support for customer provided typings for LiveObjects

ably.d.ts

@@ -2039,25 +2039,76 @@
   /**
    * Retrieves the root {@link LiveMap} object for state on a channel.
    *
+   * A type parameter can be provided to describe the structure of the LiveObjects state on the channel. By default, it uses types from the globally defined `LiveObjectsTypes` interface.
+   *
+   * You can specify custom types for LiveObjects by defining a global `LiveObjectsTypes` interface with a `root` property that conforms to {@link LiveMapType}.
+   *
+   * Example:
+   *
+   * ```typescript
+   * import { LiveCounter } from 'ably';
+   *
+   * type MyRoot = {
+   *   myTypedKey: LiveCounter;
+   * };
+   *
+   * declare global {
+   *   export interface LiveObjectsTypes {
+   *     root: MyRoot;
+   *   }
+   * }
+   * ```
+   *
    * @returns A promise which, upon success, will be fulfilled with a {@link LiveMap} object. Upon failure, the promise will be rejected with an {@link ErrorInfo} object which explains the error.
    */
-  getRoot(): Promise<LiveMap>;
+  getRoot<T extends LiveMapType = DefaultRoot>(): Promise<LiveMap<T>>;
 }
 
+declare global {
+  /**
+   * A globally defined interface that allows users to define custom types for LiveObjects.
+   */
+  export interface LiveObjectsTypes {
+    [key: string]: unknown;
+  }
+}
+
+/**
+ * Represents the type of data stored in a {@link LiveMap}.
+ * It maps string keys to scalar values ({@link StateValue}), or other LiveObjects.
+ */
+export type LiveMapType = { [key: string]: StateValue | LiveMap<LiveMapType> | LiveCounter | undefined };
+
+/**
+ * The default type for the `root` object in the LiveObjects, based on the globally defined {@link LiveObjectsTypes} interface.
+ *
+ * - If no custom types are provided in `LiveObjectsTypes`, defaults to an untyped root map representation using the {@link LiveMapType} interface.
+ * - If a `root` type exists in `LiveObjectsTypes` and conforms to the {@link LiveMapType} interface, it is used as the type for the `root` object.
+ * - If the provided `root` type does not match {@link LiveMapType}, a type error message is returned.
+ */
+export type DefaultRoot =
+  // we need a way to know when no types were provided by the user.
+  // we expect a "root" property to be set on LiveObjectsTypes interface, e.g. it won't be "unknown" anymore
+  unknown extends LiveObjectsTypes['root']
+    ? LiveMapType // no custom types provided; use the default untyped map representation for the root
+    : LiveObjectsTypes['root'] extends LiveMapType
+      ? LiveObjectsTypes['root'] // "root" property exists, and it is of an expected type, we can use this interface for the root object in LiveObjects.
+      : `Provided type definition for the "root" object in LiveObjectsTypes is not of an expected LiveMapType`;
+
 /**
  * The `LiveMap` class represents a key/value map data structure, similar to a JavaScript Map, where all changes are synchronized across clients in realtime.
  * Conflict-free resolution for updates follows Last Write Wins (LWW) semantics, meaning that if two clients update the same key in the map, the update with the most recent timestamp wins.
  *
  * Keys must be strings. Values can be another Live Object, or a primitive type, such as a string, number, boolean, or binary data (see {@link StateValue}).
  */
-export declare interface LiveMap extends LiveObject<LiveMapUpdate> {
+export declare interface LiveMap<T extends LiveMapType> extends LiveObject<LiveMapUpdate> {
   /**
    * Returns the value associated with a given key. Returns `undefined` if the key doesn't exist in a map.
    *
    * @param key - The key to retrieve the value for.
    * @returns A {@link LiveObject}, a primitive type (string, number, boolean, or binary data) or `undefined` if the key doesn't exist in a map.
    */
-  get(key: string): LiveObject | StateValue | undefined;
+  get<TKey extends keyof T & string>(key: TKey): T[TKey];
 
   /**
    * Returns the number of key/value pairs in the map.
@@ -2429,7 +2480,7 @@
    * and {@link ChannelOptions}, or returns the existing channel object.
    *
    * @experimental This is a preview feature and may change in a future non-major release.
    * This experimental method allows you to create custom realtime data feeds by selectively subscribing
    * to receive only part of the data from the channel.
    * See the [announcement post](https://pages.ably.com/subscription-filters-preview) for more information.
    *

src/plugins/liveobjects/livemap.ts

@@ -1,5 +1,6 @@
 import deepEqual from 'deep-equal';
 
+import type * as API from '../../../ably';
 import { LiveObject, LiveObjectData, LiveObjectUpdate, LiveObjectUpdateNoop } from './liveobject';
 import { LiveObjects } from './liveobjects';
 import {
@@ -45,7 +46,7 @@ export interface LiveMapUpdate extends LiveObjectUpdate {
   update: { [keyName: string]: 'updated' | 'removed' };
 }
 
-export class LiveMap extends LiveObject<LiveMapData, LiveMapUpdate> {
+export class LiveMap<T extends API.LiveMapType> extends LiveObject<LiveMapData, LiveMapUpdate> {
   constructor(
     liveObjects: LiveObjects,
     private _semantics: MapSemantics,
@@ -59,8 +60,8 @@ export class LiveMap extends LiveObject<LiveMapData, LiveMapUpdate> {
    *
    * @internal
    */
-  static zeroValue(liveobjects: LiveObjects, objectId: string): LiveMap {
-    return new LiveMap(liveobjects, MapSemantics.LWW, objectId);
+  static zeroValue<T extends API.LiveMapType>(liveobjects: LiveObjects, objectId: string): LiveMap<T> {
+    return new LiveMap<T>(liveobjects, MapSemantics.LWW, objectId);
   }
 
   /**
@@ -69,8 +70,8 @@ export class LiveMap extends LiveObject<LiveMapData, LiveMapUpdate> {
    *
    * @internal
    */
-  static fromStateObject(liveobjects: LiveObjects, stateObject: StateObject): LiveMap {
-    const obj = new LiveMap(liveobjects, stateObject.map?.semantics!, stateObject.objectId);
+  static fromStateObject<T extends API.LiveMapType>(liveobjects: LiveObjects, stateObject: StateObject): LiveMap<T> {
+    const obj = new LiveMap<T>(liveobjects, stateObject.map?.semantics!, stateObject.objectId);
     obj.overrideWithStateObject(stateObject);
     return obj;
   }
@@ -82,24 +83,25 @@ export class LiveMap extends LiveObject<LiveMapData, LiveMapUpdate> {
    * then you will get a reference to that Live Object if it exists in the local pool, or undefined otherwise.
    * If the value is not an objectId, then you will get that value.
    */
-  get(key: string): LiveObject | StateValue | undefined {
+  // force the key to be of type string as we only allow strings as key in a map
+  get<TKey extends keyof T & string>(key: TKey): T[TKey] {
     const element = this._dataRef.data.get(key);
 
     if (element === undefined) {
-      return undefined;
+      return undefined as T[TKey];
     }
 
     if (element.tombstone === true) {
-      return undefined;
+      return undefined as T[TKey];
     }
 
     // data exists for non-tombstoned elements
     const data = element.data!;
 
     if ('value' in data) {
-      return data.value;
+      return data.value as T[TKey];
     } else {
-      return this._liveObjects.getPool().get(data.objectId);
+      return this._liveObjects.getPool().get(data.objectId) as T[TKey];
     }
   }
 

src/plugins/liveobjects/liveobjects.ts

@@ -36,13 +36,18 @@ export class LiveObjects {
     this._bufferedStateOperations = [];
   }
 
-  async getRoot(): Promise<LiveMap> {
+  /**
+   * When called without a type variable, we return a default root type which is based on globally defined LiveObjects interface.
+   * A user can provide an explicit type for the getRoot method to explicitly set the LiveObjects type structure on this particular channel.
+   * This is useful when working with LiveObjects on multiple channels with different underlying data.
+   */
+  async getRoot<T extends API.LiveMapType = API.DefaultRoot>(): Promise<LiveMap<T>> {
     // SYNC is currently in progress, wait for SYNC sequence to finish
     if (this._syncInProgress) {
       await this._eventEmitter.once(LiveObjectsEvents.SyncCompleted);
     }
 
-    return this._liveObjectsPool.get(ROOT_OBJECT_ID) as LiveMap;
+    return this._liveObjectsPool.get(ROOT_OBJECT_ID) as LiveMap<T>;
   }
 
   /**

test/package/browser/template/src/ably.config.d.ts

@@ -0,0 +1,21 @@
+import { LiveCounter, LiveMap } from 'ably';
+
+type CustomRoot = {
+  numberKey: number;
+  stringKey: string;
+  booleanKey: boolean;
+  couldBeUndefined?: string;
+  mapKey?: LiveMap<{
+    foo: 'bar';
+    nestedMap?: LiveMap<{
+      baz: 'qux';
+    }>;
+  }>;
+  counterKey?: LiveCounter;
+};
+
+declare global {
+  export interface LiveObjectsTypes {
+    root: CustomRoot;
+  }
+}

test/package/browser/template/src/index-liveobjects.ts

@@ -1,7 +1,12 @@
 import * as Ably from 'ably';
 import LiveObjects from 'ably/liveobjects';
+import { CustomRoot } from './ably.config';
 import { createSandboxAblyAPIKey } from './sandbox';
 
+type ExplicitRootType = {
+  someOtherKey: string;
+};
+
 globalThis.testAblyPackage = async function () {
   const key = await createSandboxAblyAPIKey({ featureFlags: ['enableChannelState'] });
 
@@ -11,12 +16,27 @@ globalThis.testAblyPackage = async function () {
   // check liveObjects can be accessed
   const liveObjects = channel.liveObjects;
   await channel.attach();
-  // root should be a LiveMap object
-  const root: Ably.LiveMap = await liveObjects.getRoot();
+  // expect root to be a LiveMap instance with LiveObjects types defined via the global LiveObjectsTypes interface
+  // also checks that we can refer to the LiveObjects types exported from 'ably' by referencing a LiveMap interface
+  const root: Ably.LiveMap<CustomRoot> = await liveObjects.getRoot();
+
+  // check root has expected LiveMap TypeScript type methods
+  const size: number = root.size();
 
-  // check root is recognized as LiveMap TypeScript type
-  root.get('someKey');
-  root.size();
+  // check custom user provided typings via LiveObjectsTypes are working:
+  // keys on a root:
+  const aNumber: number = root.get('numberKey');
+  const aString: string = root.get('stringKey');
+  const aBoolean: boolean = root.get('booleanKey');
+  const couldBeUndefined: string | undefined = root.get('couldBeUndefined');
+  // live objects on a root:
+  const counter: Ably.LiveCounter | undefined = root.get('counterKey');
+  const map: LiveObjectsTypes['root']['mapKey'] = root.get('mapKey');
+  // check string literal types works
+  // need to use nullish coalescing as we didn't actually create any data on the root,
+  // so the next calls would fail. we only need to check that TypeScript types work
+  const foo: 'bar' = map?.get('foo')!;
+  const baz: 'qux' = map?.get('nestedMap')?.get('baz')!;
 
   // check LiveMap subscription callback has correct TypeScript types
   const { unsubscribe } = root.subscribe(({ update }) => {
@@ -31,13 +51,15 @@ globalThis.testAblyPackage = async function () {
   });
   unsubscribe();
 
-  // check LiveCounter types also behave as expected
-  const counter = root.get('randomKey') as Ably.LiveCounter | undefined;
-  // use nullish coalescing as we didn't actually create a counter object on the root,
-  // so the next calls would fail. we only need to check that TypeScript types work
-  const value: number = counter?.value();
+  // check LiveCounter type also behaves as expected
+  // same deal with nullish coalescing
+  const value: number = counter?.value()!;
   const counterSubscribeResponse = counter?.subscribe(({ update }) => {
     const shouldBeANumber: number = update.inc;
   });
   counterSubscribeResponse?.unsubscribe();
+
+  // check can provide custom types for the getRoot method, ignoring global LiveObjectsTypes interface
+  const explicitRoot: Ably.LiveMap<ExplicitRootType> = await liveObjects.getRoot<ExplicitRootType>();
+  const someOtherKey: string = explicitRoot.get('someOtherKey');
 };

test/package/browser/template/src/tsconfig.json

@@ -1,6 +1,7 @@
 {
   "include": ["**/*.ts", "**/*.tsx"],
   "compilerOptions": {
+    "strictNullChecks": true,
     "resolveJsonModule": true,
     "esModuleInterop": true,
     "module": "esnext",

typedoc.json

@@ -20,5 +20,6 @@
     "TypeAlias",
     "Variable",
     "Namespace"
-  ]
+  ],
+  "intentionallyNotExported": ["__global.LiveObjectsTypes"]
 }