61 lines
1.6 KiB
JavaScript
61 lines
1.6 KiB
JavaScript
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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// This file is meant to run inside action sandboxes
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"use strict";
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this.EventEmitter = function(driver) {
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if (!driver) {
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throw new Error("driver must be provided");
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}
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const listeners = {};
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return {
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emit(eventName, event) {
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// Fire events async
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Promise.resolve()
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.then(() => {
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if (!(eventName in listeners)) {
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driver.log(`EventEmitter: Event fired with no listeners: ${eventName}`);
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return;
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}
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// freeze event to prevent handlers from modifying it
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const frozenEvent = Object.freeze(event);
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// Clone callbacks array to avoid problems with mutation while iterating
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const callbacks = Array.from(listeners[eventName]);
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for (const cb of callbacks) {
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cb(frozenEvent);
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}
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});
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},
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on(eventName, callback) {
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if (!(eventName in listeners)) {
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listeners[eventName] = [];
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}
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listeners[eventName].push(callback);
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},
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off(eventName, callback) {
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if (eventName in listeners) {
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const index = listeners[eventName].indexOf(callback);
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if (index !== -1) {
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listeners[eventName].splice(index, 1);
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}
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}
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},
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once(eventName, callback) {
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const inner = event => {
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callback(event);
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this.off(eventName, inner);
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};
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this.on(eventName, inner);
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},
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};
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};
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