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2d43f710c5
MozReview-Commit-ID: 3ixJhRWeRpd --HG-- extra : rebase_source : 55a274b88d94d6574ab71268ca054ad93561ef7e
40 lines
1.5 KiB
JavaScript
40 lines
1.5 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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/**
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* Helpers for async functions. Async functions are generator functions that are
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* run by Tasks. An async function returns a Promise for the resolution of the
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* function. When the function returns, the promise is resolved with the
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* returned value. If it throws the promise rejects with the thrown error.
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*
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* See Task documentation at https://developer.mozilla.org/en-US/docs/Mozilla/JavaScript_code_modules/Task.jsm.
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*/
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var {Task} = require("devtools/shared/task");
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/**
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* Adds an event listener to the given element, and then removes its event
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* listener once the event is called, returning the event object as a promise.
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* @param nsIDOMElement element
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* The DOM element to listen on
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* @param String event
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* The name of the event type to listen for
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* @param Boolean useCapture
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* Should we initiate the capture phase?
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* @return Promise
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* The promise resolved with the event object when the event first
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* happens
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*/
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exports.listenOnce = function listenOnce(element, event, useCapture) {
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return new Promise(function (resolve, reject) {
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let onEvent = function (ev) {
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element.removeEventListener(event, onEvent, useCapture);
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resolve(ev);
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};
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element.addEventListener(event, onEvent, useCapture);
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});
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};
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