@nasriya/atomix
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Composable helper functions for building reliable systems
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TypeScript
import type { EventHandler, AddHandlerOptions, EventName, GlobalEventHandler } from './docs';
/**
* A flexible and lightweight event emitter class with full TypeScript support.
*
* Features:
* - Strongly typed event names and handler arguments using generics (`EventsMap`).
* - Global `'*'` handlers that receive the event name as the first argument, followed by the event's arguments.
* - `beforeAll` and `afterAll` handler types for lifecycle-style hooks.
* - One-time handlers via `on` with `{ once: true }` option (removed automatically after first execution).
* - Handler limits with overflow detection via `maxTotalHandlers` and custom overflow behavior.
* - Backward-compatible `maxHandlers` property (deprecated in favor of `maxTotalHandlers`).
*
* This implementation allows both standard event handlers and advanced lifecycle hooks,
* while supporting both typed and untyped usage.
*
* @example
* ```ts
* const emitter = new atomix.tools.EventEmitter();
*
* // Regular handler (called in the order added)
* emitter.on('data', (value) => console.log('Received:', value));
*
* // One-time handler
* emitter.on('data', (value) => console.log('Once:', value), { once: true });
*
* // Setup logic before all regular handlers
* emitter.on('data', () => console.log('Before All'), { type: 'beforeAll' });
*
* // Cleanup logic after all regular handlers
* emitter.on('data', () => console.log('After All'), { type: 'afterAll' });
*
* // Global handler receives the event name first
* emitter.on(`'*'`, (event, ...args) => console.log(`Global: ${event}`, args));
*
* // Emit the event
* await emitter.emit('data', 42);
* ```
*
* @example
* ```ts
* const emitter = new atomix.tools.EventEmitter();
*
* // Option 1: Throw an Error immediately when the limit is exceeded
* emitter.maxTotalHandlers = 2;
* emitter.onMaxHandlers(new Error('Handler limit exceeded'));
*
* emitter.on('load', () => {});
* emitter.on('load', () => {});
* emitter.on('load', () => {}); // throws immediately
*
* // Option 2: Use a custom function to handle overflows (debounced)
* emitter.onMaxHandlers((eventName) => {
* console.warn(`Handler overflow on event: ${eventName}`);
* });
* ```
*
* @template EventsMap - Optional type map for event names and handler signatures. Defaults to `{}` for untyped usage.
*
* @since v1.0.8
*/
export declare class EventEmitter<EventsMap extends Record<string, EventHandler> = {}> {
#private;
/**
* Emits an event, triggering all registered handlers for the given event name.
*
* This method supports both **typed** and **untyped** emitters:
*
* - In a **typed emitter** (`EventEmitter<{ load: () => void; data: (value: number) => void }>`),
* the `eventName` parameter is restricted to the keys of the provided map,
* and the `args` are automatically typed according to the event's parameters.
*
* - In an **untyped emitter** (`EventEmitter` with default `{}`), `eventName` can be any string,
* and `args` are of type `any[]`.
*
* Global (`'*'`) handlers are triggered on every emit and receive the actual event name as the first argument.
*
* Handlers are invoked in the following order for each `emit` call:
* 1. The `beforeAll` handler (if set) runs before all `normal` handlers.
* 2. All `normal` handlers (in the order they were registered).
* 3. The `afterAll` handler (if set) runs after all `normal` handlers.
*
* `beforeAll` and `afterAll` are singleton handlers — only one of each may be set per event name.
* They are not removed automatically and are executed on every `emit` call.
*
* `normal` handlers may be marked as `once`, in which case they are removed after their first invocation.
*
* @template E - The event name type; inferred automatically.
* @param eventName - The name of the event to emit, or `'*'` for global handlers. Must be a non-empty string.
* @param args - Arguments to pass to all applicable handlers. Automatically typed for typed emitters.
*
* @throws {TypeError} If the event name is not a string.
* @throws {RangeError} If the event name is an empty string.
*
* @example
* // Untyped emitter
* const emitter = new EventEmitter();
* emitter.on('*', (event, ...args) => console.log(`Global: ${event}`, args));
* await emitter.emit('load', true);
*
* @example
* // Typed emitter
* type MyEvents = { load: (ok: boolean) => void; data: (value: number) => void };
* const typedEmitter = new EventEmitter<MyEvents>();
* typedEmitter.on('data', (value) => console.log('Data:', value));
* typedEmitter.on('*', (event, ...args) => console.log(`Global: ${event}`, args));
* await typedEmitter.emit('data', 42); // value typed as number
*
* @since v1.0.8
*/
emit<E extends EventName<EventsMap>>(eventName: [E] extends [never] ? string : E, ...args: [E] extends [never] ? any[] : Parameters<EventsMap[E]>): Promise<void>;
/**
* Adds a handler to an event.
*
* This method supports both **typed** and **untyped** event emitters.
*
* ### Typed vs untyped emitters
* - In a **typed emitter** (`EventEmitter<{ load: () => void; data: (value: number) => void }>`),
* `eventName` is restricted to the keys of the provided map, and `handler` is fully type-safe.
* - In an **untyped emitter** (`EventEmitter` with the default `{}`), `eventName` may be any string.
*
* ### Global handlers (`'*'`)
* Passing `'*'` as the event name registers a **global handler** that listens to all events.
* The handler receives the actual event name as the first argument, followed by the event arguments.
*
* ### Handler types
* - `"normal"`: Runs on every emit (default)
* - `"beforeAll"`: Runs before all normal handlers for the event
* - `"afterAll"`: Runs after all normal handlers for the event
*
* ### Intentional no-op handlers
* This method explicitly supports passing `atomix.utils.noop` as the handler.
*
* Doing so **preserves the semantic intent of attaching a handler** without:
* - allocating a new function,
* - storing it in memory,
* - or creating misleading empty implementations.
*
* No-op handlers are ignored internally while keeping the event registration intentional and explicit.
*
* @template E - The event name type (inferred automatically).
* @param eventName - The name of the event to add the handler to, or `'*'` for a global handler.
* @param handler - The handler function for the event, or `atomix.utils.noop` to intentionally register a no-op.
* @param options - Optional configuration for the handler. Defaults to `{ once: false, type: 'normal' }`.
* @param options.once - If true, the handler is removed after being called once.
* @param options.type - The type of handler. One of `"normal"`, `"beforeAll"`, or `"afterAll"`.
*
* @throws {TypeError} If `eventName` is not a string, or `handler` is not a function.
* @throws {RangeError} If `eventName` is an empty string, or `options.type` is invalid.
*
* @returns The EventEmitter instance, allowing method chaining.
*
* @example
* // Intentional placeholder handler
* emitter.on('ready', atomix.utils.noop);
*
* @example
* // Typed emitter
* type Events = { ready: () => void };
* const typedEmitter = new EventEmitter<Events>();
* typedEmitter.on('ready', atomix.utils.noop);
*
* @since v1.0.8
*/
on<E extends EventName<EventsMap> | '*'>(eventName: [Exclude<E, '*'>] extends [never] ? string : E, handler: E extends '*' ? GlobalEventHandler<EventsMap> : EventsMap[E], options?: AddHandlerOptions): this;
/**
* Registers a custom handler for the "max handlers exceeded" event.
*
* When the number of handlers for an event exceeds the maximum allowed, this handler is called with the event name as an argument.
*
* - If a **function** is provided, it is debounced (100ms) to prevent excessive calls during rapid handler additions.
* - If an **Error** object is provided, it will be thrown immediately when the limit is exceeded.
*
* @param handler - A function to call when the maximum number of handlers is exceeded, or an Error to throw.
* @returns The EventEmitter instance, allowing method chaining.
*
* @throws {TypeError} If the handler is not a function or an Error instance.
*
* @example
* ```ts
* const emitter = new atomix.tools.EventEmitter();
*
* // Throw an error when the max handlers limit is exceeded
* emitter.onMaxHandlers(new Error('Handler limit exceeded'));
*
* // Or provide a custom function
* emitter.onMaxHandlers((eventName) => {
* console.warn(`Handler overflow on event: ${eventName}`);
* });
* ```
*
* @since v1.0.8
*/
onMaxHandlers(handler: ((eventName: string) => any) | Error): this;
/**
* Cleans up any internal resources used by this instance.
*
* Specifically, cancels any pending debounced handlers (such as
* warnings about maximum handlers) to prevent timers from
* keeping the process alive or causing side effects after disposal.
*
* This method should be called when the instance is no longer needed,
* such as during test teardown or object cleanup.
*
* @since v1.0.15
*/
dispose(): void;
/**
* Retrieves the maximum number of event handlers allowed for this EventEmitter instance.
*
* The value is a positive integer or Infinity. If set to Infinity, there is no limit to the number of handlers.
*
* @returns {number} The maximum number of handlers. A positive integer or Infinity.
* @since v1.0.24
*/
get maxTotalHandlers(): number;
/**
* Sets the maximum number of event handlers allowed for this EventEmitter instance.
*
* The value must be a positive integer or Infinity. If set to Infinity, there is no limit to the number of handlers.
*
* @param {number} value The maximum number of handlers. Must be a positive integer or Infinity.
* @throws {TypeError} If the provided value is not a number or not an integer.
* @throws {RangeError} If the provided value is not greater than 0.
* @since v1.0.24
*/
set maxTotalHandlers(value: number);
/**
* Retrieves the maximum number of event handlers allowed for this EventEmitter instance.
*
* The value is a positive integer or Infinity. If set to Infinity, there is no limit to the number of handlers.
*
* @returns {number} The maximum number of handlers. A positive integer or Infinity.
* @deprecated Use {@link maxTotalHandlers} getter/setter instead.
* @since v1.0.8
*/
get maxHandlers(): number;
/**
* Sets the maximum number of event handlers allowed for this EventEmitter instance.
*
* The value must be a positive integer or Infinity. If set to Infinity, there is no limit to the number of handlers.
*
* @param {number} value The maximum number of handlers. Must be a positive integer or Infinity.
* @throws {TypeError} If the provided value is not a number or not an integer.
* @throws {RangeError} If the provided value is not greater than 0.
* @deprecated Use {@link maxTotalHandlers} getter/setter instead.
* @since v1.0.8
*/
set maxHandlers(value: number);
/**
* Retrieves the total number of event handlers registered with this EventEmitter instance.
* @returns {number} The total number of event handlers.
* @since v1.0.8
*/
get handlersCount(): number;
/**
* Retrieves the names of all registered events for this EventEmitter instance.
*
* @returns {string[]} An array of event names.
* @since v1.0.8
*/
get eventNames(): string[];
/**
* A collection of methods to remove event handlers.
*
* This allows removing specific handlers or clearing all handlers from one or more events.
*
* @example
* ```ts
* const emitter = new EventEmitter();
* const handler = () => console.log('Hello');
*
* emitter.on('greet', handler);
* emitter.remove.handler('greet', handler); // Removes just this one
* ```
*
* @example
* ```ts
* emitter.on('load', () => {});
* emitter.on('error', () => {});
* emitter.remove.allHandlers(); // Removes everything
* ```
*
* @example
* ```ts
* emitter.remove.allHandlers('load'); // Removes all "load" handlers only
* ```
*
* @since v1.0.8
*/
readonly remove: {
/**
* Removes a specified event handler for a given event name.
*
* @param eventName - The name of the event for which the handler should be removed.
* @param handler - The handler function to remove.
* @returns {boolean} True if the handler was successfully removed, otherwise false.
* @throws {TypeError} Throws if the event name is not a string or the handler is not a function.
* @since v1.0.8
*/
handler: (eventName: string, handler: EventHandler) => boolean;
/**
* Removes all handlers for a given event name or all events if no name is specified.
*
* @param eventName - (Optional) The name of the event for which handlers should be removed. If not provided, handlers for all events are removed.
* @returns {boolean} True if any handlers were removed, otherwise false.
* @throws {TypeError} Throws if the event name is not a string.
* @throws {RangeError} Throws if the event name is an empty string.
* @since v1.0.8
*/
allHandlers: (eventName?: string) => boolean;
};
}
export default EventEmitter;