promise | Polyfill of ES2015 's Promise | Reactive Programming library
kandi X-RAY | promise Summary
kandi X-RAY | promise Summary
const promise = new Promise(executor) // 创建Promise的语法.
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Currently covering the most popular Java, JavaScript and Python libraries. See a Sample of promise
promise Key Features
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Community Discussions
Trending Discussions on promise
QUESTION
const set = firebase.firestore().collection("workoutExercises").doc(firebase.auth().currentUser.uid).get()
console.log(set)
...ANSWER
Answered 2021-Jun-15 at 23:56Firebase calls like this are asynchronous, meaning they don't return immediately. In Javascript, you can deal with this in a couple of different ways, using async/await
or Promises
.
Here's an example using a Promise
:
QUESTION
How do I get the URL of the current tab in the background service worker in MV3?
Here's what I have:
...ANSWER
Answered 2021-Jun-15 at 21:40You function getTab
seems not right, you are currently trying to query on the url. Not on the query options. The following function should work.
QUESTION
I have a for loop which calls a few times to database API. These calls return data for a menu, but when I try to map array I can't do it because array is empty.
First scenario:
...ANSWER
Answered 2021-Jun-15 at 17:22You most likely don't want to call getData on every render, so you should store the response somewhere, it might be in the component state:
QUESTION
So I currently doing some unit test for an Angular application using Jasmine and Karma. I'm having a problem with a unit test that must open a modal, change some value of the form and save it. Everthing is doing well until it reaches inside the promise for the open()
of my modal service and call saveAttribute()
function.
The expects seems to have been called saveAttribute()
successfully, but none of the functions inside of it are never called, even the hasValidRegex()
function, despite being the first thing called in the saveAttribute()
function. I also tried using a console log at the beginning of the saveAttribute()
function but it never reaches it and print nothing apart of the function begin successfully called. Am I missing something?
.spec file
...ANSWER
Answered 2021-Jun-15 at 12:44I think I know the issue. The issue is this:
QUESTION
In the following code:
...ANSWER
Answered 2021-Feb-27 at 09:23There are 2 separate queues for handling of the callbacks. A macro and a micro queue. setTimeout
enqueues an item in the macro queue, while promise resolution - to the micro queue. The currently executing macro task(the main script itself in this case) is executed synchronously, line by line until it is finished. The moment it is finished, the loop executes everything queued in the microtask queue before continuing with the next item from the macro queue(which in your case is the console.log("hello")
queued from the setTimeout
).
Basically, the flow looks like this:
- Script starts executing.
MacrotaskQueue: [], MicrotaskQueue: [].
setTimeout(() => console.log("hello"), 0);
is encountered which leads to pushing a new item in the macrotask queue.
MacrotaskQueue: [console.log("hello")
], MicrotaskQueue: [].
Promise.resolve('Success!').then(console.log)
is read. Promise resolves toSuccess!
immediately andconsole.log
callback gets enqueued to the microtask queue.
MacrotaskQueue: [console.log("hello")
], MicrotaskQueue: [console.log('Success!')
].
- The script finishes executing so it checks if there is something in the microtask queue before proceeding with the next task from the macro queue.
console.log('Success!')
is pulled from the microtask queue and executed.
MacrotaskQueue: [console.log("hello")
], MicrotaskQueue: [].
- Script checks again if there is something else in the microtask queue. There is none, so it fetches the first available task from the macrotask queue and executes it, namely -
console.log("hello")
.
MacrotaskQueue: [], MicrotaskQueue: [].
- After the script finishes executing the
console.log("hello")
, it once again checks if there is anything in the microtask queue. It is empty, so it checks the macrotask queue. It is empty as well so everything queued is executed and the script finishes.
This is a simplified explanation, though, as it can get trickier. The microtask queue normally handles mainly promise callbacks, but you can enqueue code on it yourself. The newly added items in the microtask queue will still be executed before the next macrotask item. Also, microtasks can enqueue other microtasks, which can lead to an endless loop of processing microtasks.
Some useful reference resources:
QUESTION
My intention is to get the weather data for the selected country, passing selectedCountry.capital to the query, so it is displayed the weather from current country capital when the data of a country is displayed.
The problem is my code tries to render the weather data before the weather array is fetched, resulting in an error.
TypeError: Cannot read property 'temperature' of undefined
I get the array data
...ANSWER
Answered 2021-Jun-15 at 11:54Simply use Optional chaining here:
QUESTION
I have a problem with creating a function that will stop all the code until it finishes. I thought making async/await. In that function I should make fetch, but it says promise {}, when I return the result CODE:
...ANSWER
Answered 2021-Jun-13 at 13:45When you add async prior to the function then this means that the function will return a promise in response, and in order to work with that result You need to do something like this
QUESTION
I setup a new Gatsby project through the installer but when I try to create a new file in /src/pages
, but if then I go to that route, the browser says
Preparing requested page
in loop. In the browser console it outputs:
...ANSWER
Answered 2021-Mar-18 at 06:11Have you tried renaming your home.js
to index.js
?
After that, clean the cache by gatsby clean
.
QUESTION
I have a self updating list of orders that is scrollable. This is the parent component, where list is updated on a timer of 2 minutes, setup like so:
...ANSWER
Answered 2021-Jun-11 at 13:10You could try using element.scrollTop
to save the position of the scrollbar and then use the saved value to set the scrollTop property to where it was when the timed function is called.
(https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollTop?retiredLocale=it - https://www.javascripttutorial.net/dom/css/get-and-set-scroll-position-of-an-element/)
QUESTION
I have a firebase function that sends an email, updates a record on another collection and creates an account on another API service when a new user is created. The whole operation runs for 2 minutes but I think it can be optimized further. I'm also new to async await so I don't really know how to use it properly.
...ANSWER
Answered 2021-Jun-15 at 08:17If your functions are declared async
, you need to use the await
keyword when calling them. And consequently you need to declare the Cloud Function itself as async
.
So the following should do the trick:
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