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70 lines
1.6 KiB
70 lines
1.6 KiB
/*
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Copyright 2019 Google LLC
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Use of this source code is governed by an MIT-style
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license that can be found in the LICENSE file or at
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https://opensource.org/licenses/MIT.
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*/
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import '../_version.mjs';
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/**
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* A minimal `EventTarget` shim.
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* This is necessary because not all browsers support constructable
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* `EventTarget`, so using a real `EventTarget` will error.
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* @private
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*/
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class EventTargetShim {
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/**
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* Creates an event listener registry
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*
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* @private
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*/
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constructor() {
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// A registry of event types to listeners.
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this._eventListenerRegistry = {};
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}
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/**
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* @param {string} type
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* @param {Function} listener
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* @private
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*/
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addEventListener(type, listener) {
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this._getEventListenersByType(type).add(listener);
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}
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/**
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* @param {string} type
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* @param {Function} listener
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* @private
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*/
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removeEventListener(type, listener) {
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this._getEventListenersByType(type).delete(listener);
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}
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/**
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* @param {Event} event
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* @private
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*/
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dispatchEvent(event) {
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event.target = this;
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this._getEventListenersByType(event.type).forEach(
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(listener) => listener(event));
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}
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/**
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* Returns a Set of listeners associated with the passed event type.
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* If no handlers have been registered, an empty Set is returned.
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*
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* @param {string} type The event type.
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* @return {Set} An array of handler functions.
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* @private
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*/
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_getEventListenersByType(type) {
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return this._eventListenerRegistry[type] =
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(this._eventListenerRegistry[type] || new Set());
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}
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}
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export {EventTargetShim};
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