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event_utils.js
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/* Copyright 2012 Mozilla Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
const WaitOnType = {
EVENT: "event",
TIMEOUT: "timeout",
};
/**
* @typedef {Object} WaitOnEventOrTimeoutParameters
* @property {Object} target - The event target, can for example be:
* `window`, `document`, a DOM element, or an {EventBus} instance.
* @property {string} name - The name of the event.
* @property {number} delay - The delay, in milliseconds, after which the
* timeout occurs (if the event wasn't already dispatched).
*/
/**
* Allows waiting for an event or a timeout, whichever occurs first.
* Can be used to ensure that an action always occurs, even when an event
* arrives late or not at all.
*
* @param {WaitOnEventOrTimeoutParameters}
* @returns {Promise} A promise that is resolved with a {WaitOnType} value.
*/
async function waitOnEventOrTimeout({ target, name, delay = 0 }) {
if (
typeof target !== "object" ||
!(name && typeof name === "string") ||
!(Number.isInteger(delay) && delay >= 0)
) {
throw new Error("waitOnEventOrTimeout - invalid parameters.");
}
const { promise, resolve } = Promise.withResolvers();
const ac = new AbortController();
function handler(type) {
ac.abort(); // Remove event listener.
clearTimeout(timeout);
resolve(type);
}
const evtMethod = target instanceof EventBus ? "_on" : "addEventListener";
target[evtMethod](name, handler.bind(null, WaitOnType.EVENT), {
signal: ac.signal,
});
const timeout = setTimeout(handler.bind(null, WaitOnType.TIMEOUT), delay);
return promise;
}
/**
* Simple event bus for an application. Listeners are attached using the `on`
* and `off` methods. To raise an event, the `dispatch` method shall be used.
*/
class EventBus {
#listeners = Object.create(null);
/**
* @param {string} eventName
* @param {function} listener
* @param {Object} [options]
*/
on(eventName, listener, options = null) {
this._on(eventName, listener, {
external: true,
once: options?.once,
signal: options?.signal,
});
}
/**
* @param {string} eventName
* @param {function} listener
* @param {Object} [options]
*/
off(eventName, listener, options = null) {
this._off(eventName, listener);
}
/**
* @param {string} eventName
* @param {Object} data
*/
dispatch(eventName, data) {
const eventListeners = this.#listeners[eventName];
if (!eventListeners || eventListeners.length === 0) {
return;
}
let externalListeners;
// Making copy of the listeners array in case if it will be modified
// during dispatch.
for (const { listener, external, once } of eventListeners.slice(0)) {
if (once) {
this._off(eventName, listener);
}
if (external) {
(externalListeners ||= []).push(listener);
continue;
}
listener(data);
}
// Dispatch any "external" listeners *after* the internal ones, to give the
// viewer components time to handle events and update their state first.
if (externalListeners) {
for (const listener of externalListeners) {
listener(data);
}
externalListeners = null;
}
}
/**
* @ignore
*/
_on(eventName, listener, options = null) {
let rmAbort = null;
if (options?.signal instanceof AbortSignal) {
const { signal } = options;
if (signal.aborted) {
console.error("Cannot use an `aborted` signal.");
return;
}
const onAbort = () => this._off(eventName, listener);
rmAbort = () => signal.removeEventListener("abort", onAbort);
signal.addEventListener("abort", onAbort);
}
const eventListeners = (this.#listeners[eventName] ||= []);
eventListeners.push({
listener,
external: options?.external === true,
once: options?.once === true,
rmAbort,
});
}
/**
* @ignore
*/
_off(eventName, listener, options = null) {
const eventListeners = this.#listeners[eventName];
if (!eventListeners) {
return;
}
for (let i = 0, ii = eventListeners.length; i < ii; i++) {
const evt = eventListeners[i];
if (evt.listener === listener) {
evt.rmAbort?.(); // Ensure that the `AbortSignal` listener is removed.
eventListeners.splice(i, 1);
return;
}
}
}
}
/**
* NOTE: Only used in the Firefox build-in pdf viewer.
*/
class FirefoxEventBus extends EventBus {
#externalServices;
#globalEventNames;
#isInAutomation;
constructor(globalEventNames, externalServices, isInAutomation) {
super();
this.#globalEventNames = globalEventNames;
this.#externalServices = externalServices;
this.#isInAutomation = isInAutomation;
}
dispatch(eventName, data) {
if (typeof PDFJSDev !== "undefined" && !PDFJSDev.test("MOZCENTRAL")) {
throw new Error("Not implemented: FirefoxEventBus.dispatch");
}
super.dispatch(eventName, data);
if (this.#isInAutomation) {
const detail = Object.create(null);
if (data) {
for (const key in data) {
const value = data[key];
if (key === "source") {
if (value === window || value === document) {
return; // No need to re-dispatch (already) global events.
}
continue; // Ignore the `source` property.
}
detail[key] = value;
}
}
const event = new CustomEvent(eventName, {
bubbles: true,
cancelable: true,
detail,
});
document.dispatchEvent(event);
}
if (this.#globalEventNames?.has(eventName)) {
this.#externalServices.dispatchGlobalEvent({
eventName,
detail: data,
});
}
}
}
export { EventBus, FirefoxEventBus, waitOnEventOrTimeout, WaitOnType };