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* EventTarget - Provides the [EventTarget](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget) interface
*/
class CornerstoneEventTarget implements EventTarget {
private listeners;
private debouncedListeners;
constructor() {
this.listeners = {};
this.debouncedListeners = {};
}
public reset() {
this.listeners = {};
this.debouncedListeners = {};
}
public addEventListenerOnce(type, callback) {
// Create a wrapper function to encapsulate the original callback
const onceWrapper = (event) => {
// Remove the listener after its first invocation
this.removeEventListener(type, onceWrapper);
// Call the original callback
callback.call(this, event);
};
// Add the wrapper as the listener
this.addEventListener(type, onceWrapper);
}
public addEventListener(type, callback) {
if (!this.listeners[type]) {
this.listeners[type] = [];
}
// prevent multiple callbacks from firing
if (this.listeners[type].indexOf(callback) !== -1) {
return;
}
this.listeners[type].push(callback);
}
/**
* Adds a debounced event listener to the event target.
*
* @param type - The type of the event to listen for.
* @param callback - The callback function to be executed when the event is triggered.
* @param delay - The delay in milliseconds before the callback is invoked after the last event.
*/
public addEventListenerDebounced(type, callback, delay) {
// Ensure the dictionary for the type exists
this.debouncedListeners[type] = this.debouncedListeners[type] || {};
const debouncedCallbacks = this.debouncedListeners[type];
// Check if there's already a debounced version of this callback registered
if (!debouncedCallbacks[callback]) {
const handle = (event) => {
// Clear any existing timeout to reset the debounce timer
if (debouncedCallbacks[callback]) {
clearTimeout(debouncedCallbacks[callback].timeoutId);
}
// Set a new timeout
debouncedCallbacks[callback].timeoutId = setTimeout(() => {
callback.call(this, event);
}, delay);
};
// Store the handle and initial timeoutId (null initially)
debouncedCallbacks[callback] = {
original: callback,
handle,
timeoutId: null,
};
// Register the debounced handler
this.addEventListener(type, handle);
}
}
/**
* Removes a debounced event listener from the event target.
*
* @param type - The type of the event.
* @param callback - The callback function to be removed.
*/
public removeEventListenerDebounced(type, callback) {
if (
this.debouncedListeners[type] &&
this.debouncedListeners[type][callback]
) {
const debounced = this.debouncedListeners[type][callback];
this.removeEventListener(type, debounced.handle);
clearTimeout(debounced.timeoutId);
delete this.debouncedListeners[type][callback];
}
}
public removeEventListener(type, callback) {
if (!this.listeners[type]) {
return;
}
const stack = this.listeners[type];
const stackLength = stack.length;
for (let i = 0; i < stackLength; i++) {
if (stack[i] === callback) {
stack.splice(i, 1);
return;
}
}
}
dispatchEvent(event) {
if (!this.listeners[event.type]) {
//console.warn(`Skipping dispatch since there are no listeners for ${event.type}`);
return;
}
const stack = this.listeners[event.type].slice();
const stackLength = stack.length;
for (let i = 0; i < stackLength; i++) {
try {
stack[i].call(this, event);
} catch (error) {
console.error(`error in event listener of type: ${event.type}`, error);
}
}
return !event.defaultPrevented;
}
}
/**
* EventTarget - Provides the [EventTarget](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget) interface
*/
const eventTarget = new CornerstoneEventTarget();
export default eventTarget;
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