tiny-essentials
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Collection of small, essential scripts designed to be used across various projects. These simple utilities are crafted for speed, ease of use, and versatility.
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JavaScript
/**
* A generic event listener callback function.
*
* @callback handler
* @param {...any} payload - The data payload passed when the event is triggered.
* @returns {void}
*/
/**
* TinyEvents provides a minimalistic event emitter system similar to Node.js's EventEmitter,
* enabling components to subscribe to, emit, and manage events and their listeners.
*
* Features include:
* - Adding/removing event listeners (`on`, `off`, `offAll`, `offAllTypes`)
* - One-time listeners (`once`)
* - Emitting events (`emit`)
* - Listener inspection and limits (`listenerCount`, `listeners`, `eventNames`)
* - Maximum listener control (`setMaxListeners`, `getMaxListeners`)
*
* This class is useful for lightweight, dependency-free publish/subscribe event handling
* within modular JavaScript applications.
*
* @class
*/
class TinyEvents {
/** @type {Map<string, { handler: handler; config: { once: boolean } }[]>} */
#listeners = new Map();
/** @type {number} */
#maxListeners = 10;
/** @type {boolean} */
#throwMaxListeners = false;
/**
* Enables or disables throwing an error when the maximum number of listeners is exceeded.
*
* @param {boolean} shouldThrow - If true, an error will be thrown when the max is exceeded.
*/
setThrowOnMaxListeners(shouldThrow) {
if (typeof shouldThrow !== 'boolean')
throw new TypeError('setThrowOnMaxListeners(value): value must be a boolean');
this.#throwMaxListeners = shouldThrow;
}
/**
* Checks whether an error will be thrown when the max listener limit is exceeded.
*
* @returns {boolean} True if an error will be thrown, false if only a warning is shown.
*/
getThrowOnMaxListeners() {
return this.#throwMaxListeners;
}
///////////////////////////////////////////////////
/**
* Internal method to prepend a listener with options.
*
* @param {string} event - Event name.
* @param {handler} handler - The callback function.
* @param {Object} [settings={}] - Optional settings.
* @param {boolean} [settings.once=false] - If the listener should be executed once.
*/
#prepend(event, handler, { once = false } = {}) {
let eventData = this.#listeners.get(event);
if (!Array.isArray(eventData)) {
eventData = [];
this.#listeners.set(event, eventData);
}
eventData.unshift({ handler, config: { once } });
const max = this.#maxListeners;
if (max > 0 && eventData.length > max) {
const warnMessage = `Possible memory leak detected. ${eventData.length} "${event}" listeners added. ` +
`Use setMaxListeners() to increase limit.`;
if (!this.#throwMaxListeners)
console.warn(warnMessage);
else
throw new Error(warnMessage);
}
}
/**
* Adds a listener to the beginning of the listeners array for the specified event.
*
* @param {string} event - Event name.
* @param {handler} handler - The callback function.
*/
prependListener(event, handler) {
if (typeof event !== 'string')
throw new TypeError('prepend(event, handler): event name must be a string');
if (typeof handler !== 'function')
throw new TypeError('prepend(event, handler): handler must be a function');
this.#prepend(event, handler);
}
/**
* Adds a one-time listener to the beginning of the listeners array for the specified event.
*
* @param {string} event - Event name.
* @param {handler} handler - The callback function.
* @returns {handler} - The wrapped handler used internally.
*/
prependListenerOnce(event, handler) {
if (typeof event !== 'string')
throw new TypeError('prependOnceListener(event, handler): event name must be a string');
if (typeof handler !== 'function')
throw new TypeError('prependOnceListener(event, handler): handler must be a function');
/** @type {handler} */
const wrapped = (...args) => {
this.off(event, wrapped);
handler(...args);
};
this.#prepend(event, wrapped, { once: true });
return wrapped;
}
////////////////////////////////////////////////////////////
/**
* Adds a event listener.
*
* @param {string} event - Event name, such as 'onScrollBoundary' or 'onAutoScroll'.
* @param {handler} handler - Callback function to be called when event fires.
* @param {Object} [settings={}] - Optional settings.
* @param {boolean} [settings.once=false] - This is a once event.
*/
#on(event, handler, { once = false } = {}) {
let eventData = this.#listeners.get(event);
if (!Array.isArray(eventData)) {
eventData = [];
this.#listeners.set(event, eventData);
}
eventData.push({ handler, config: { once } });
// Warn if listener count exceeds the max allowed
const max = this.#maxListeners;
if (max > 0 && eventData.length > max) {
const warnMessage = `Possible memory leak detected. ${eventData.length} "${event}" listeners added. ` +
`Use setMaxListeners() to increase limit.`;
if (!this.#throwMaxListeners)
console.warn(warnMessage);
else
throw new Error(warnMessage);
}
}
/**
* Adds a event listener.
*
* @param {string} event - Event name, such as 'onScrollBoundary' or 'onAutoScroll'.
* @param {handler} handler - Callback function to be called when event fires.
*/
on(event, handler) {
if (typeof event !== 'string')
throw new TypeError('on(event, handler): event name must be a string');
if (typeof handler !== 'function')
throw new TypeError('on(event, handler): handler must be a function');
return this.#on(event, handler);
}
/**
* Registers an event listener that runs only once, then is removed.
*
* @param {string} event - Event name, such as 'onScrollBoundary' or 'onAutoScroll'.
* @param {handler} handler - The callback function to run on event.
* @returns {handler} - The wrapped version of the handler.
*/
once(event, handler) {
if (typeof event !== 'string')
throw new TypeError('The event name must be a string.');
if (typeof handler !== 'function')
throw new TypeError('once(event, handler): handler must be a function');
/** @type {handler} */
const wrapped = (e) => {
this.off(event, wrapped);
if (typeof handler === 'function')
handler(e);
};
this.#on(event, wrapped, { once: true });
return wrapped;
}
/**
* Adds a event listener.
*
* @param {string} event - Event name, such as 'onScrollBoundary' or 'onAutoScroll'.
* @param {handler} handler - Callback function to be called when event fires.
*/
appendListener(event, handler) {
return this.on(event, handler);
}
/**
* Registers an event listener that runs only once, then is removed.
*
* @param {string} event - Event name, such as 'onScrollBoundary' or 'onAutoScroll'.
* @param {handler} handler - The callback function to run on event.
* @returns {handler} - The wrapped version of the handler.
*/
appendListenerOnce(event, handler) {
return this.once(event, handler);
}
///////////////////////////////////////////////
/**
* Removes a previously registered event listener.
*
* @param {string} event - The name of the event to remove the handler from.
* @param {handler} handler - The specific callback function to remove.
*/
off(event, handler) {
if (typeof event !== 'string')
throw new TypeError('off(event, handler): event name must be a string');
if (typeof handler !== 'function')
throw new TypeError('off(event, handler): handler must be a function');
const listeners = this.#listeners.get(event);
if (!Array.isArray(listeners))
return;
const index = listeners.findIndex((listener) => listener.handler === handler);
if (index !== -1)
listeners.splice(index, 1);
// Optionally clean up empty arrays (optional)
if (listeners.length === 0)
this.#listeners.delete(event);
}
/**
* Removes all event listeners of a specific type from the element.
*
* @param {string} event - The event type to remove (e.g. 'onScrollBoundary').
*/
offAll(event) {
if (typeof event !== 'string')
throw new TypeError('The event name must be a string.');
this.#listeners.delete(event);
}
/**
* Removes all event listeners of all types from the element.
*/
offAllTypes() {
this.#listeners.clear();
}
/////////////////////////////////////////////
/**
* Returns the number of listeners for a given event.
*
* @param {string} event - The name of the event.
* @returns {number} Number of listeners for the event.
*/
listenerCount(event) {
if (typeof event !== 'string')
throw new TypeError('listenerCount(event): event name must be a string');
const listeners = this.#listeners.get(event);
return Array.isArray(listeners) ? listeners.length : 0;
}
/**
* Returns a copy of the array of listeners for the specified event.
*
* @param {string} event - The name of the event.
* @returns {handler[]} Array of listener functions.
*/
listeners(event) {
if (typeof event !== 'string')
throw new TypeError('listeners(event): event name must be a string');
const listeners = this.#listeners.get(event);
return Array.isArray(listeners)
? [...listeners]
.filter((listener) => !listener.config.once)
.map((listener) => listener.handler)
: [];
}
/**
* Returns a copy of the array of listeners for the specified event.
*
* @param {string} event - The name of the event.
* @returns {handler[]} Array of listener functions.
*/
onceListeners(event) {
if (typeof event !== 'string')
throw new TypeError('onceListeners(event): event name must be a string');
const listeners = this.#listeners.get(event);
return Array.isArray(listeners)
? [...listeners]
.filter((listener) => listener.config.once)
.map((listener) => listener.handler)
: [];
}
/**
* Returns a copy of the internal listeners array for the specified event,
* including wrapper functions like those used by `.once()`.
* @param {string | symbol} event - The event name.
* @returns {handler[]} An array of raw listener functions.
*/
allListeners(event) {
if (typeof event !== 'string')
throw new TypeError('allListeners(event): event name must be a string');
const listeners = this.#listeners.get(event);
return Array.isArray(listeners) ? [...listeners].map((listener) => listener.handler) : [];
}
/**
* Returns an array of event names for which there are registered listeners.
*
* @returns {string[]} Array of registered event names.
*/
eventNames() {
return [...this.#listeners.keys()];
}
/**
* Emits an event, triggering all registered handlers for that event.
*
* @param {string} event - The event name to emit.
* @param {...any} payload - Optional data to pass to each handler.
* @returns {boolean} True if any listeners were called, false otherwise.
*/
emit(event, ...payload) {
if (typeof event !== 'string')
throw new TypeError('emit(event, data): event name must be a string');
const listeners = this.#listeners.get(event);
if (!Array.isArray(listeners) || listeners.length === 0)
return false;
// Call all listeners with the provided data
listeners.forEach((listener) => listener.handler(...payload));
return true;
}
///////////////////////////////////
/**
* Sets the maximum number of listeners per event before a warning is shown.
*
* @param {number} n - The maximum number of listeners.
*/
setMaxListeners(n) {
if (!Number.isInteger(n) || n < 0)
throw new TypeError('setMaxListeners(n): n must be a non-negative integer');
this.#maxListeners = n;
}
/**
* Gets the maximum number of listeners allowed per event.
*
* @returns {number} The maximum number of listeners.
*/
getMaxListeners() {
return this.#maxListeners;
}
}
export default TinyEvents;