gecko-dev/remote/Observer.jsm

31 lines
842 B
JavaScript

/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
"use strict";
var EXPORTED_SYMBOLS = ["Observer"];
const {Services} = ChromeUtils.import("resource://gre/modules/Services.jsm");
class Observer {
static observe(type, observer) {
Services.obs.addObserver(observer, type);
}
static unobserve(type, observer) {
Services.obs.removeObserver(observer, type);
}
static once(type, observer = () => {}) {
return new Promise(resolve => {
const wrappedObserver = (first, ...rest) => {
Observer.unobserve(type, wrappedObserver);
observer.call(first, ...rest);
resolve();
};
Observer.observe(type, wrappedObserver);
});
}
}