/**
* ListenerHandler class: handles add/removing and firing listeners.
*
* @see https://developer.mozilla.org/en-US/docs/Web/API/EventTarget#example
*/
export class ListenerHandler {
/**
* listeners.
*
* @type {object}
*/
#listeners = {};
/**
* Add an event listener.
*
* @param {string} type The event type.
* @param {object} callback The method associated with the provided
* event type, will be called with the fired event.
*/
add(type, callback) {
// create array if not present
if (typeof this.#listeners[type] === 'undefined') {
this.#listeners[type] = [];
}
// add callback to listeners array
this.#listeners[type].push(callback);
}
/**
* Remove an event listener.
*
* @param {string} type The event type.
* @param {object} callback The method associated with the provided
* event type.
*/
remove(type, callback) {
// check if the type is present
if (typeof this.#listeners[type] === 'undefined') {
return;
}
// remove from listeners array
for (let i = 0; i < this.#listeners[type].length; ++i) {
if (this.#listeners[type][i] === callback) {
this.#listeners[type].splice(i, 1);
}
}
}
/**
* Fire an event: call all associated listeners with the input event object.
*
* @param {object} event The event to fire.
*/
fireEvent = (event) => {
// check if they are listeners for the event type
if (typeof this.#listeners[event.type] === 'undefined') {
return;
}
// fire events from a copy of the listeners array
// to avoid interference from possible add/remove
const stack = this.#listeners[event.type].slice();
for (let i = 0; i < stack.length; ++i) {
stack[i](event);
}
};
}