61 lines
1.9 KiB
JavaScript
61 lines
1.9 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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"use strict";
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module.metadata = {
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"stability": "unstable"
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};
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const { Cc, Ci, Cr } = require("chrome");
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const { emit, on, off } = require("./core");
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const { addObserver, removeObserver } = Cc["@mozilla.org/observer-service;1"].
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getService(Ci.nsIObserverService);
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const { when: unload } = require("../system/unload");
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// Simple class that can be used to instantiate event channel that
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// implements `nsIObserver` interface. It's will is used by `observe`
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// function as observer + event target. It basically proxies observer
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// notifications as to it's registered listeners.
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function ObserverChannel() {}
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Object.freeze(Object.defineProperties(ObserverChannel.prototype, {
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QueryInterface: {
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value: function(iid) {
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if (!iid.equals(Ci.nsIObserver) &&
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!iid.equals(Ci.nsISupportsWeakReference) &&
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!iid.equals(Ci.nsISupports))
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throw Cr.NS_ERROR_NO_INTERFACE;
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return this;
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}
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},
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observe: {
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value: function(subject, topic, data) {
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emit(this, "data", {
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type: topic,
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target: subject,
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data: data
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});
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}
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}
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}));
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function observe(topic) {
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let observerChannel = new ObserverChannel();
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// Note: `nsIObserverService` will not hold a weak reference to a
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// observerChannel (since third argument is `true`). There for if it
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// will be GC-ed with all it's event listeners once no other references
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// will be held.
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addObserver(observerChannel, topic, true);
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// We need to remove any observer added once the add-on is unloaded;
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// otherwise we'll get a "dead object" exception.
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// See: https://bugzilla.mozilla.org/show_bug.cgi?id=1001833
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unload(() => removeObserver(observerChannel, topic));
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return observerChannel;
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}
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exports.observe = observe;
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