Typing

If you are using TypeScript in your project, you can leverage LiveObjects’ built-in TypeScript support to ensure type safety and enable autocompletion when working with objects on a channel.

Global ObjectsTypes interface

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You can type objects on all your channels by defining a global ObjectsTypes interface. If you only want to type the root object for a specific channel, see the Typing channel.objects.getRoot() section below.

Define the ObjectsTypes interface in a type declaration file. You can create a file named ably.config.d.ts in the root of your application:

JavaScript v2.9

// file: ably.config.d.ts
import { LiveCounter, LiveMap } from 'ably';


// Define dedicated types and export them for reuse in your application
export type MyCustomRoot = {
  reactions: LiveMap<{
    hearts: LiveCounter;
    likes: LiveCounter;
  }>;
};


declare global {
  export interface ObjectsTypes {
    root: MyCustomRoot;
  }
}


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This enables TypeScript to infer the correct types when accessing and mutating LiveObjects:

JavaScript v2.9

// LiveMap<{ reactions: LiveMap<{ hearts: LiveCounter; likes: LiveCounter }> }>
const root = await channel.objects.getRoot();


// LiveMap<{ hearts: LiveCounter; likes: LiveCounter }>
const reactions = root.get('reactions');


// LiveCounter
const likes = reactions.get('likes');


reactions.set('hearts', 1); // Error: Argument of type 'number' is not assignable to parameter of type 'LiveCounter'.ts(2345)


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Typing channel.objects.getRoot()

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You can pass a type parameter directly to the channel.objects.getRoot<T>() method call to type the root object for a channel explicitly:

JavaScript v2.9

// Define types for different root objects
type ReactionsRoot = {
  hearts: LiveCounter;
  likes: LiveCounter;
};


type PollsRoot = {
  currentPoll: LiveMap;
};


// LiveMap<{ hearts: LiveCounter; likes: LiveCounter }>
const reactionsRoot = await reactionsChannel.objects.getRoot<ReactionsRoot>();


// LiveMap<{ currentPoll: LiveMap }>
const pollsRoot = await pollsChannel.objects.getRoot<PollsRoot>();


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Typing channel.objects.getRoot<T>() is particularly useful when your application uses multiple channels, each with a different object structure.

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