浅念
82 lines
2.8 KiB
JavaScript
82 lines
2.8 KiB
JavaScript
/**
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Licensed to the Apache Software Foundation (ASF) under one
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or more contributor license agreements. See the NOTICE file
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distributed with this work for additional information
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regarding copyright ownership. The ASF licenses this file
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to you under the Apache License, Version 2.0 (the
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"License"); you may not use this file except in compliance
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with the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, either express or implied. See the License for the
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specific language governing permissions and limitations
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under the License.
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*/
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const EventEmitter = require('events').EventEmitter;
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const MAX_LISTENERS = 20;
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const INSTANCE_KEY = Symbol.for('org.apache.cordova.common.CordovaEvents');
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let EVENTS_RECEIVER = null;
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class CordovaEventEmitter extends EventEmitter {
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/**
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* Sets up current instance to forward emitted events to another EventEmitter
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* instance.
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*
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* @param {EventEmitter} [eventEmitter] The emitter instance to forward
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* events to. Falsy value, when passed, disables forwarding.
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*/
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forwardEventsTo (eventEmitter) {
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// If no argument is specified disable events forwarding
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if (!eventEmitter) {
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EVENTS_RECEIVER = undefined;
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return;
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}
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if (!(eventEmitter instanceof EventEmitter)) {
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throw new Error('Cordova events can be redirected to another EventEmitter instance only');
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}
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// CB-10940 Skipping forwarding to self to avoid infinite recursion.
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// This is the case when the modules are npm-linked.
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if (this !== eventEmitter) {
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EVENTS_RECEIVER = eventEmitter;
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} else {
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// Reset forwarding if we are subscribing to self
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EVENTS_RECEIVER = undefined;
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}
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}
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/**
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* Sets up current instance to forward emitted events to another EventEmitter
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* instance.
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*
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* @param {EventEmitter} [eventEmitter] The emitter instance to forward
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* events to. Falsy value, when passed, disables forwarding.
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*/
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emit (eventName, ...args) {
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if (EVENTS_RECEIVER) {
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EVENTS_RECEIVER.emit(eventName, ...args);
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}
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return super.emit(eventName, ...args);
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}
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}
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// This singleton instance pattern is based on the ideas from
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// https://derickbailey.com/2016/03/09/creating-a-true-singleton-in-node-js-with-es6-symbols/
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if (Object.getOwnPropertySymbols(global).indexOf(INSTANCE_KEY) === -1) {
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const events = new CordovaEventEmitter();
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events.setMaxListeners(MAX_LISTENERS);
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global[INSTANCE_KEY] = events;
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}
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module.exports = global[INSTANCE_KEY];
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