gecko-dev/devtools/shared/async-utils.js

38 строки
1.4 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";
/**
* Helpers for async functions. Async functions are generator functions that are
* run by Tasks. An async function returns a Promise for the resolution of the
* function. When the function returns, the promise is resolved with the
* returned value. If it throws the promise rejects with the thrown error.
*
* See Task documentation at https://developer.mozilla.org/en-US/docs/Mozilla/JavaScript_code_modules/Task.jsm.
*/
/**
* Adds an event listener to the given element, and then removes its event
* listener once the event is called, returning the event object as a promise.
* @param Element element
* The DOM element to listen on
* @param String event
* The name of the event type to listen for
* @param Boolean useCapture
* Should we initiate the capture phase?
* @return Promise
* The promise resolved with the event object when the event first
* happens
*/
exports.listenOnce = function listenOnce(element, event, useCapture) {
return new Promise(function(resolve, reject) {
let onEvent = function(ev) {
element.removeEventListener(event, onEvent, useCapture);
resolve(ev);
};
element.addEventListener(event, onEvent, useCapture);
});
};