Medplum

// SPDX-FileCopyrightText: Copyright Orangebot, Inc. and Medplum contributors // SPDX-License-Identifier: Apache-2.0 /* * Based on: https://developer.mozilla.org/en-US/docs/Web/API/EventTarget */ export interface Event { readonly type: string; readonly defaultPrevented?: boolean; } export type EventListener = (e: Event) => void; export class EventTarget { private readonly listeners: Record<string, EventListener[]>; constructor() { this.listeners = {}; } addEventListener(type: string, callback: EventListener): void { if (!this.listeners[type]) { this.listeners[type] = []; } this.listeners[type].push(callback); } removeEventListener(type: string, callback: EventListener): void { const array = this.listeners[type]; if (!array) { return; } for (let i = 0; i < array.length; i++) { if (array[i] === callback) { array.splice(i, 1); return; } } } dispatchEvent(event: Event): boolean { const array = this.listeners[event.type]; if (array) { for (const listener of array) { listener.call(this, event); } } return !event.defaultPrevented; } removeAllListeners(): void { // @ts-expect-error Normally listeners is read-only. In this case we are dumping all listeners this.listeners = {}; } /** * Gets the number of listeners for the provided Event type. * @param type - The name of the Event type. * @returns The number of listeners for this Event type. */ listenerCount(type: string): number { return this.listeners[type]?.length ?? 0; } } export class TypedEventTarget<TEvents extends Record<string, Event>> { private readonly emitter = new EventTarget(); dispatchEvent<TEventType extends keyof TEvents>(event: TEvents[TEventType]): void { this.emitter.dispatchEvent(event); } addEventListener<TEventType extends keyof TEvents>( type: TEventType, handler: (event: TEvents[TEventType]) => void ): void { this.emitter.addEventListener(type as string, handler as any); } removeEventListener<TEventType extends keyof TEvents>( type: TEventType, handler: (event: TEvents[TEventType]) => void ): void { this.emitter.removeEventListener(type as string, handler as any); } removeAllListeners(): void { this.emitter.removeAllListeners(); } /** * Gets the number of listeners for the provided Event type. * @param type - The name of the Event type. * @returns The number of listeners for this Event type. */ listenerCount<TEventType extends keyof TEvents>(type: TEventType): number { return this.emitter.listenerCount(type as string); } }