@nasriya/atomix
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Composable helper functions for building reliable systems
498 lines (497 loc) • 20.2 kB
JavaScript
import valueIs from '../../valueIs.js';
import commonUtils from '../../domains/utils/utils.js';
import recordsUtils from '../../domains/data-types/record/records-utils.js';
/**
* A flexible and lightweight event emitter class that supports advanced features like:
* - `beforeAll` and `afterAll` handler types
* - One-time (`once`) handlers
* - Handler limits with overflow detection
* - Custom max-handler overflow behavior
*
* This implementation allows both standard event handlers and lifecycle-style hooks around them.
*
* @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' });
*
* // Emit the event
* await emitter.emit('data', 42);
* ```
*
* @example
* ```ts
* // Custom behavior when handler count exceeds limit
* emitter.maxHandlers = 2;
* emitter.onMaxHandlers((eventName) => {
* throw new Error(`Handler overflow on ${eventName}`);
* });
*
* emitter.on('load', () => {});
* emitter.on('load', () => {});
* emitter.on('load', () => {}); // throws
* ```
*
* @since v1.0.8
*/
export class EventEmitter {
#_events = new Map();
#_stats = {
handlers: { number: 0, max: 10 },
};
#_helpers = {
getEvents: (eventName) => {
if (this.#_events.has(eventName)) {
return this.#_events.get(eventName);
}
const events = {
name: eventName,
handlersNumber: 0,
handlers: {
before: undefined,
after: undefined,
normal: {
index: 0,
handlers: new Map(),
onceHandlers: new Map(),
},
}
};
this.#_events.set(eventName, events);
return events;
},
onMaxHandlers: {
builtInHandler: commonUtils.debounceSync(() => {
if (this.#_stats.handlers.number > this.#_stats.handlers.max) {
console.warn(`[WARN] The maximum number of handlers has been reached (${this.#_stats.handlers.max}). Current number of handlers: ${this.#_stats.handlers.number}.`);
}
}, 1000),
customHandler: null,
check: (eventName) => {
const customHandler = this.#_helpers.onMaxHandlers.customHandler;
if (customHandler instanceof Error) {
if (this.#_stats.handlers.number > this.#_stats.handlers.max) {
const newErr = new Error();
newErr.message = `[WARN] ${customHandler.message}`;
newErr.cause = customHandler.cause;
throw newErr;
}
return;
}
;
const builtInHandler = this.#_helpers.onMaxHandlers.builtInHandler;
const toInvoke = customHandler !== null ? customHandler : builtInHandler;
toInvoke(eventName);
}
},
updateEventHandlersNum: (events, delta) => {
events.handlersNumber += delta;
this.#_stats.handlers.number += delta;
if (events.handlersNumber === 0) {
events.handlers.normal.index = 0;
}
},
};
#_runner = {
processEvents: async (events, ...args) => {
if (events.handlers.before) {
await this.#_runner.runHandler(events.handlers.before, events.name, ...args);
}
// Handle normal events
for (let i = 0; i < events.handlers.normal.index; i++) {
const handler = (events.handlers.normal.handlers.get(i) || events.handlers.normal.onceHandlers.get(i));
if (!handler) {
continue;
}
await this.#_runner.runHandler(handler, events.name, ...args);
}
if (events.handlers.after) {
await this.#_runner.runHandler(events.handlers.after, events.name, ...args);
}
const onceHandlersCount = events.handlers.normal.onceHandlers.size;
this.#_helpers.updateEventHandlersNum(events, -onceHandlersCount);
events.handlers.normal.onceHandlers.clear();
},
runHandler: async (handler, eventName, ...args) => {
try {
await handler(...args);
}
catch (error) {
this.#_runner.onError(error, eventName);
}
},
onError: (err, eventName) => {
console.error(`[HandlerError] (${eventName})`, err);
},
};
/**
* Emits an event, triggering all registered handlers for the given event name.
*
* 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 special 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 will be removed
* after their first invocation.
*
* Global (`'*'`) handlers are triggered on every emit and receive the actual event
* name as their first argument.
*
* @async
* @param eventName - The name of the event to emit. Must be a non-empty string.
* @param args - Arguments to pass to all applicable handler functions.
*
* @throws {TypeError} If the event name is not a string.
* @throws {RangeError} If the event name is an empty string.
*
* @example
* ```ts
* const emitter = new EventEmitter();
*
* emitter.on('data', (value) => console.log('Normal:', value));
* emitter.on('data', () => console.log('Before All'), { type: 'beforeAll' });
* emitter.on('data', () => console.log('After All'), { type: 'afterAll' });
*
* await emitter.emit('data', 123);
* // Output:
* // Before All
* // Normal: 123
* // After All
* ```
*
* @example
* ```ts
* emitter.on('*', (event, ...args) => {
* console.log(`Global handler: ${event}`, args);
* });
*
* await emitter.emit('load', true);
* // Output:
* // Global handler: load [true]
* ```
*
* @since v1.0.8
*/
async emit(eventName, ...args) {
if (!valueIs.string(eventName)) {
throw new TypeError(`The provided event name (${eventName}) is not a string.`);
}
if (eventName.length === 0) {
throw new RangeError(`The provided event name (${eventName}) is an empty string.`);
}
const globalEvents = this.#_helpers.getEvents('*');
const namedEvents = eventName === '*' ? undefined : this.#_helpers.getEvents(eventName);
if (namedEvents) {
await this.#_runner.processEvents(namedEvents, ...args);
}
if (globalEvents) {
await this.#_runner.processEvents(globalEvents, ...args);
}
}
/**
* Adds a handler to an event.
*
* @param eventName - The name of the event to add the handler to.
* @param handler - The handler function to add.
* @param options - (Optional) Additional configuration options for the handler. If not provided, defaults to `{ once: false, type: 'normal' }`.
* @param options.once - (Optional) If true, the handler is removed after being called once. Defaults to false.
* @param options.type - (Optional) The type of event handler to add. One of "before", "after", or "normal". Defaults to "normal".
*
* @throws {TypeError} Throws if the event name is not a string or the handler is not a function.
* @throws {RangeError} Throws if the event name is an empty string or the type is not a valid event type.
*
* @returns The EventEmitter instance.
* @since v1.0.8
*/
on(eventName, handler, options) {
const configs = {
once: false,
type: 'normal',
};
if (!valueIs.string(eventName)) {
throw new TypeError(`The provided event name (${eventName}) is not a string.`);
}
if (eventName.length === 0) {
throw new RangeError(`The provided event name (${eventName}) is an empty string.`);
}
if (typeof handler !== 'function') {
throw new TypeError(`The provided handler (${handler}) is not a function.`);
}
if (options !== undefined) {
if (!valueIs.record(options)) {
throw new TypeError(`The provided options (${options}) is not a record.`);
}
if (recordsUtils.hasOwnProperty(options, 'once')) {
if (typeof options.once !== 'boolean') {
throw new TypeError(`The "once" property of the provided options (${options}) is not a boolean.`);
}
configs.once = options.once;
}
if (recordsUtils.hasOwnProperty(options, 'type')) {
if (!valueIs.string(options.type)) {
throw new TypeError(`The "type" property of the provided options (${options}) is not a string.`);
}
if (!['beforeAll', 'afterAll', 'normal'].includes(options.type)) {
throw new RangeError(`The "type" property of the provided options (${options}) is not a valid event type.`);
}
configs.type = options.type;
}
}
const events = this.#_helpers.getEvents(eventName);
if (configs.type === 'beforeAll' || configs.type === 'afterAll') {
if (configs.type === 'beforeAll') {
events.handlers.before = handler;
}
if (configs.type === 'afterAll') {
events.handlers.after = handler;
}
}
else {
const id = events.handlers.normal.index++;
events.handlers.normal[configs.once ? 'onceHandlers' : 'handlers'].set(id, handler);
}
this.#_helpers.updateEventHandlersNum(events, 1);
this.#_helpers.onMaxHandlers.check(eventName);
return 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.
*
* The handler is debounced to prevent excessive calls when the maximum number of handlers is exceeded multiple times in quick succession.
*
* @param handler - A function to call when the maximum number of handlers is exceeded or an error to throw.
* @returns The EventEmitter instance.
* @throws {TypeError} If the handler is not a function or an error.
* @since v1.0.8
*/
onMaxHandlers(handler) {
const isFunction = typeof handler === 'function';
const isError = handler instanceof Error;
if (!isFunction && !isError) {
throw new TypeError(`The provided handler (${handler}) is not a function or an error.`);
}
if (isError) {
this.#_helpers.onMaxHandlers.customHandler = handler;
}
if (isFunction) {
this.#_helpers.onMaxHandlers.customHandler = commonUtils.debounceSync((eventName) => {
if (this.#_stats.handlers.number <= this.#_stats.handlers.max) {
return;
}
handler(eventName);
}, 100, {
onError: (err) => { throw err; }
});
}
return 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() {
const { builtInHandler, customHandler } = this.#_helpers.onMaxHandlers;
builtInHandler?.cancel();
if (typeof customHandler !== 'function') {
return;
}
customHandler?.cancel();
}
/**
* 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 v1.0.8
*/
get maxHandlers() { return this.#_stats.handlers.max; }
/**
* 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 v1.0.8
*/
set maxHandlers(value) {
if (!valueIs.number(value)) {
throw new TypeError('maxHandlers must be a number');
}
if (value === Infinity) {
this.#_stats.handlers.max = value;
return;
}
if (value <= 0) {
throw new RangeError('maxHandlers must be greater than 0');
}
if (!valueIs.integer(value)) {
throw new TypeError('maxHandlers must be an integer');
}
this.#_stats.handlers.max = value;
}
/**
* 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() { return this.#_stats.handlers.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() { return Array.from(this.#_events.keys()).filter(name => name !== '*'); }
/**
* 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
*/
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, handler) => {
if (!valueIs.string(eventName)) {
throw new TypeError(`The provided event name (${eventName}) is not a string.`);
}
if (eventName.length === 0) {
throw new RangeError(`The provided event name (${eventName}) is an empty string.`);
}
if (typeof handler !== 'function') {
throw new TypeError(`The provided handler (${handler}) is not a function.`);
}
const events = this.#_events.get(eventName);
if (!events) {
return false;
}
const removed = (() => {
const isBefore = events.handlers.before === handler;
const isAfter = events.handlers.after === handler;
if (isBefore || isAfter) {
if (isBefore) {
events.handlers.before = undefined;
}
if (isAfter) {
events.handlers.after = undefined;
}
return true;
}
for (let i = 0; i < events.handlers.normal.index; i++) {
const storedHandler = events.handlers.normal.handlers.get(i);
if (storedHandler === handler) {
events.handlers.normal.handlers.delete(i);
return true;
}
const storedOnceHandler = events.handlers.normal.onceHandlers.get(i);
if (storedOnceHandler === handler) {
events.handlers.normal.onceHandlers.delete(i);
return true;
}
}
return false;
})();
if (removed) {
this.#_helpers.updateEventHandlersNum(events, -1);
}
return removed;
},
/**
* 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) => {
if (eventName !== undefined) {
if (!valueIs.string(eventName)) {
throw new TypeError(`The provided event name (${eventName}) is not a string.`);
}
if (eventName.length === 0) {
throw new RangeError(`The provided event name (${eventName}) is an empty string.`);
}
}
const events = eventName ? [this.#_events.get(eventName)] : Array.from(this.#_events.values());
let anyRemoved = false;
for (const event of events) {
if (!event) {
continue;
}
let removed = 0;
if (event.handlers.before) {
removed++;
}
if (event.handlers.after) {
removed++;
}
removed += event.handlers.normal.handlers.size + event.handlers.normal.onceHandlers.size;
this.#_events.delete(event.name);
this.#_helpers.updateEventHandlersNum(event, -removed);
anyRemoved = removed > 0;
}
return anyRemoved;
}
};
}
export default EventEmitter;