gecko-dev/remote/Sync.jsm
Andreas Tolfsen 1601819536 bug 1523104: remote: introduce MessagePromise sync primitive; r=ochameau
Makes the code slightly more pleasant to read.
2019-03-08 16:27:17 +00:00

103 lines
3.0 KiB
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 = [
"DOMContentLoadedPromise",
"EventPromise",
"MessagePromise",
];
const {Services} = ChromeUtils.import("resource://gre/modules/Services.jsm");
/**
* Wait for a single event to be fired on a specific EventListener.
*
* The returned promise is guaranteed to not be called before the
* next event tick after the event listener is called, so that all
* other event listeners for the element are executed before the
* handler is executed. For example:
*
* const promise = new EventPromise(element, "myEvent");
* // same event tick here
* await promise;
* // next event tick here
*
* @param {EventListener} listener
* Object which receives a notification (an object that implements
* the Event interface) when an event of the specificed type occurs.
* @param {string} type
* Case-sensitive string representing the event type to listen for.
* @param {boolean?} [false] options.capture
* Indicates the event will be despatched to this subject,
* before it bubbles down to any EventTarget beneath it in the
* DOM tree.
* @param {boolean?} [false] options.wantsUntrusted
* Receive synthetic events despatched by web content.
* @param {boolean?} [false] options.mozSystemGroup
* Determines whether to add listener to the system group.
*
* @return {Promise.<Event>}
*
* @throws {TypeError}
*/
function EventPromise(listener, type, options = {
capture: false,
wantsUntrusted: false,
mozSystemGroup: false,
}) {
if (!listener || !("addEventListener" in listener)) {
throw new TypeError();
}
if (typeof type != "string") {
throw new TypeError();
}
if (("capture" in options && typeof options.capture != "boolean") ||
("wantsUntrusted" in options && typeof options.wantsUntrusted != "boolean") ||
("mozSystemGroup" in options && typeof options.mozSystemGroup != "boolean")) {
throw new TypeError();
}
options.once = true;
return new Promise(resolve => {
listener.addEventListener(type, event => {
Services.tm.dispatchToMainThread(() => resolve(event));
}, options);
});
}
function DOMContentLoadedPromise(window, options = {mozSystemGroup: true}) {
if (window.document.readyState == "complete") {
return Promise.resolve();
}
return new EventPromise(window, "DOMContentLoaded", options);
}
/**
* Awaits a single IPC message.
*
* @param {nsIMessageSender} target
* @param {string} name
*
* @return {Promise}
*
* @throws {TypeError}
* If target is not an nsIMessageSender.
*/
function MessagePromise(target, name) {
if (!(target instanceof Ci.nsIMessageSender)) {
throw new TypeError();
}
return new Promise(resolve => {
const onMessage = (...args) => {
target.removeMessageListener(name, onMessage);
resolve(...args);
};
target.addMessageListener(name, onMessage);
});
}