Delegate

• Delegate
  • Overview
  • Modes
  • API Reference
  • Example Usage

The Delegate system provides a type-safe way to implement the observer pattern, allowing multiple subscribers to react to events or method calls.

Overview

A Delegate maintains a list of subscribers and can invoke them either sequentially or in parallel. It supports both synchronous and asynchronous callbacks.

Modes

The Delegate can operate in two modes:

Mode	Description
DelegateMode.SEQUENTIAL	(Default) Invokes subscribers one after another, awaiting each if it returns a promise.
DelegateMode.PARALLEL	Invokes all subscribers concurrently using Promise.allSettled.

API Reference

Delegate<Arguments>

• constructor(mode?: DelegateMode): Initializes a new delegate with the specified mode.
• subscribe(cb: DelegateCallback<Arguments>): DelegateRevoke: Subscribes a callback and returns a function to unsubscribe.
• invoke(...args: Arguments): Promise<void>: Invokes all subscribers with the provided arguments.
• dispose(): void: Removes all subscribers.

Example Usage

import {Delegate, DelegateMode} from 'vue-mvvm';

// Define a delegate that accepts a string argument
const onMessage = new Delegate<[string]>(DelegateMode.SEQUENTIAL);

// Subscribe to messages
const revoke = onMessage.subscribe((msg) => {
    console.log(`Received: ${msg}`);
});

// Invoke the delegate
await onMessage.invoke("Hello World");

// Unsubscribe
revoke();

Usage in ViewModels

Delegates are often used to expose events from services or between ViewModels.

export class ChatService {
    public readonly onNewMessage = new Delegate<[Message]>();
}

export class ChatViewModel extends ViewModel {
    private readonly chatService: ChatService;

    constructor() {
        super();
        this.chatService = this.ctx.getService(ChatService);
    }

    protected mounted() {
        // Subscribe and ensure we cleanup on unmount
        const revoke = this.chatService.onNewMessage.subscribe(msg => this.handleMessage(msg));

        // Note: In a real scenario, you might want to track this revoke 
        // to call it in beforeUnmount.
    }
}