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31 lines
842 B
JavaScript
31 lines
842 B
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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var EXPORTED_SYMBOLS = ["Observer"];
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const {Services} = ChromeUtils.import("resource://gre/modules/Services.jsm");
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class Observer {
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static observe(type, observer) {
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Services.obs.addObserver(observer, type);
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}
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static unobserve(type, observer) {
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Services.obs.removeObserver(observer, type);
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}
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static once(type, observer = () => {}) {
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return new Promise(resolve => {
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const wrappedObserver = (first, ...rest) => {
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Observer.unobserve(type, wrappedObserver);
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observer.call(first, ...rest);
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resolve();
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};
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Observer.observe(type, wrappedObserver);
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});
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}
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}
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