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/* 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
"use strict";
/**
* Helpers for async functions. 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.
*/
/**
* 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) {
const onEvent = function (ev) {
element.removeEventListener(event, onEvent, useCapture);
resolve(ev);
};
element.addEventListener(event, onEvent, useCapture);
});
};
// Return value when `safeAsyncMethod` catches an error.
const SWALLOWED_RET = Symbol("swallowed");
/**
* Wraps the provided async method in a try/catch block.
* If an error is caught while running the method, check the provided condition
* to decide whether the error should bubble or not.
*
* @param {Function} asyncFn
* The async method to wrap.
* @param {Function} shouldSwallow
* Function that will run when an error is caught. If it returns true,
* the error will be swallowed. Otherwise, it will bubble up.
* @param {Mixed} retValue
* Optional value to return when an error is caught and is swallowed.
* @return {Function} The wrapped method.
*/
exports.safeAsyncMethod = function (
asyncFn,
shouldSwallow,
retValue = SWALLOWED_RET
) {
return async function (...args) {
try {
const ret = await asyncFn(...args);
return ret;
} catch (e) {
if (shouldSwallow()) {
console.warn("Async method failed in safeAsyncMethod", e);
return retValue;
}
throw e;
}
};
};