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JavaScript Async Guides

The JavaScript Async function is one of the most powerful, yet sometimes unintuitive concepts in JavaScript. Hopefully you will have a better grip over async and async await once you dive into these guides.

This is a collection of top and trending guides written by the community on subjects related to JavaScript Async concepts. For all things JavaScript, check out the JavaScript tag! Please contribute more posts like this to help your fellow developer in need.

React Hooks with Async-Await

Till now this is our simple code for getting the final search value in state 'query'. Now we make our custom Async hook to search on google Api's.

💡 React Hooks: async function in the useEffect

When you're new to React Hooks, you may notice that you get warnings and bugs if you use an async function inside the useEffect Hook. Let's find out why this happens.

Cancellable async functions in JavaScript

(This post explains how to use generators to wrangle duplicate calls to async functions. Check out this gist for the final approach or read on to learn more! 🎓)

Homebrew React Hooks: useAsyncEffect Or How to Handle Async Operations with useEffect

Async functions lack cancelability. We can use generator functions for mimicking cancelable async functions. I created a library for writing async effects: useAsyncEffect on Github

Implementing react-select Async with React Hooks and applying Pagination

This tutorial is about implementing the React Component react-select with Async AJAX request and pagination applied. As we won't implement the BackEnd code, we can just use the OpenSource API:

Vue.js Pattern for Async Requests: Using Renderless Components

To cut right to the meat, jump to The Async Renderless Component.

The Proper Way to Write Async Constructors in JavaScript

In this article, we will discuss the limitations of the various ways we've attempted to emulate async constructors. Once we've established the shortcomings, I will demonstrate what I have found to be the proper async constructor pattern in JavaScript.

A key difference between .then() and async-await in JavaScript

When learning all about fetch() and the Promise fetch() returns, I was introduced to JavaScript's .then()function as a means of handling the asynchronous nature of a Promise. So, what's the deal with async and await? Is it just syntactic sugar to avoid .then()'s callback hell? Searching "async vs .then" in google produces front page results such as this stackoverflow post. But, as we all come to know on our coding journey, the devil is in the details...

Cleaning up Async Functions in React's useEffect Hook (Unsubscribing)

So now we have gone through the basics as a recap, let's take a look at the issue with async functions.

Capture error and data in async-await without try-catch

One of the things that took the Javascript community by storm was the introduction of async-await. It was simple and looked a lot better than the then-catch of Promises and also more readable and debuggable than the callback hell. But one thing that bothered me was the usage of try-catch. At first I thought it isn't a problem but as fate would have it I was working on chained API calls and the problem cropped up where each API call has specific error message that had to be printed. I realized soon that I was creating a try-catch hell.

Using Async-Await with SuperTest

In this post, I will cover how async-awaits can help us write better and clean tests. async-await makes working with asynchronous programming a bit easier for us, let's see how it works -

Why async code is so damn confusing (and a how to make it easy)

There are literally hundreds of questions and articles about async and a lot of them sound something like this:

Callback vs Promises vs Async Await

Now, the first restaurant example represents an asynchronous process because you did not have to wait, the waiter takes the order from one table and goes to the next table to take the order. While the second example restaurant represents a synchronous operation because you had to wait until the resource (waiter in this case) can proceed with you. This is the single, most fundamental difference between sync and async processes.

Introducing the Async Debounce pattern

That is the main dish. It's where we actually do the work. Here it's symbolized by the doTheSearch() function, but you can do any async work you want to do.

Testing-library: avoid these mistakes in async tests

Never forget to await for async functions or return promises from the test (jest will wait for this promise to be resolved in this case). Otherwise, you may end up running tests that always pass.

Synchronous HTTP calls in Angular using Async and Await

Observables in Angular offer significant benefits over other techniques for event handling, asynchronous programming, and handling multiple values. But some times we may want to wait for the response from previous HTTP call or load default settings for an application. In that case, we use Async and Await functions to achieve this. This blog post explains the steps and provides code samples. As usual complete code uploaded to Github

React - async image loading

Before we start, I would highly recommend you to check out runnable example for the solution on our website: React - async image loading

Las promesas y async await lógicamente no son iguales. Y te explico el porqué

¿Alguna vez te has preguntado el por qué existe async await si ya se tiene las promesas? Muchos desarrolladores ya están usando esta funcionalidad. Sin embargo, no saben cómo funciona o cómo es diferente de las promesas. Eso es exactamente lo que abarcará este post. Empezaremos recordando por qué llegaron las promesas y cómo es que funciona, luego será el turno de async await y su funcionamiento. Finalmente veremos un ejemplo de cómo aplicar estas dos formas de manejar la asíncronia en conjunto.

Promise & Async await in JavaScript.

The async functions and the await keyword, added in ECMAScript 2017.

These features basically act as syntactic sugar on top of promises, making asynchronous code easier to write and to read afterwards.

Using request/success/failure pattern in Redux to handle async actions

When any async action or API call is made, there are mainly 3 states:

Preventing unhandled promise rejections in async functions

It turns out that the problem was that in all my test cases actions.afterRequestActions was resolving/ being rejected before activeRequestHandler.response is resolved. Meanwhile, in production afterRequestActions contains logic that can take substantially longer to execute. I have also learned that even if you declare a try..catch block for your async function, if it resolves before it is await-ted, then you will get an unhandled rejection, i.e.

Why all the Suspense? Understanding Async Consistency in JavaScript Frameworks

So let's stay in the past. The tricky part is how do we trigger the upcoming async requests if we don't apply any data changes?

Dynamic and async components made easy with Vue.js

You can check the latest updated version of this article at lobotuerto's notes - Dynamic and async components made easy with Vue.js.

ES2018. Real-life simple usage of async iteration: get paginated data from REST APIs in 20 lines of code

In this post I am NOT going to explain what are async iterators or iterators. You can get those explanations in here or here

Angular Concepts in React: The Async Pipe

One of my favorite tools in the Angular framework is the Async pipe. It allows me to render the latest value of an Observable to the screen. The component will then re-render to display the next value of the observable each time it receives a new notification. Finally, the subscription to the observable will be disposed of as soon as the component dismouns. Automatically! It allows me to build my asynchronous code in neat, RxJs streams.

Mongoose calls examples with async-await in an ExpressJS API

This post was originally published at Cleaner code in NodeJs with async-await - Mongoose calls example

Handling async operations and promise values in javascript arrays

To the main reason we are here, I have often had difficulties in the past using these array methods whenever my callback had to be an async function or handle a Promise. I eventually got to figure it out and put this piece together in case anyone else faces these struggles. I will give examples using the map and reduce methods. The knowledge from both can be applied to the other methods which are quite similar.

The saga of async JavaScript: Generators

Generators are a very different type of thing. They don't meet this run-to-completion rule at all. On the surface, it should have brought quite a bit of chaos into our code. But it appears that they provide yet another way to solve our problems, although the way itself might look a bit strange. One way to explain Generators would be to say that in current JavaScript they let us define a state machine - a series of flow from one state to another state with an ability to declaratively list those transitions. I am sure that most of you created quite a few state machines and you might not even know that it is called this way. Previously, there were a lot of efforts and time involved in implementing state machines using available tools in JavaScript. We often used a closure to maintain a current and previous state in a function making all of those transitions, but the code was getting complex, and writing it was time-consuming as well. Generators are adding syntactic sugar which lets you solve the same problem in a lot easier and clear way. But how does that help with async code? To get there, we first need to get a good grasp on the internal plumbings of Generators.

Use async / await with Javascript's .map() and other high-order functions

The .map() algorithm applies an async callback to each element of an array, creating promises as it does. However, the returned result  by .map() is no promise, but an array of promises.

Using RxJS Timer to Provide Periodic Async Data

We will be using the rxjs timer operator to transform this into a stream of data and provide it directly to our template with help of the async pipe.

Vue Academy #6: Async update queue

I will begin by explain you what is going on if we don't use an async update queue.

How to use async function in useEffect?

Before exploring different ways to make async calls inside useEffect let's discuss the problem behind it.

Fetch with Promise.all and async / await

How to combine Promise.all with fetch, map, async and await to make a cleaner code

DIY: Writing custom React Hooks to perform async operations

This article is about creating your own React Hooks to perform async operations. As an example, we will create a custom useFetch Hook to make API calls.

Build pagination with ES6 async generators and iterables

yield the response. The return will be a promise to be consumed by the async caller using .next()(we'll get to that in the next section)

Handling Pagination with Async Iterators

You can extract the code that handles the pagination by converting the whole block into an async function. But since functions can only return data once, you're stuck until all the requests are finished before you can return albums and use it.

My Take on Async JavaScript Promises with Concurrency Limit

There's other things regarding Promises that I won't go over. Such as try/catch which basically lets you wrap your Async operations in a try block and it will call catch if anything inside the block goes wrong.

About async functions

Async functions are great, especially if you have to call multiple functions in a row that return promises. With async / await, code becomes easier to reason about for humans, because the data flow mimics synchronous code, which is what we are used to reading.

When to use async and defer attributes in a script tag and why it is important

Do you know the importance of defer and async attributes in the script tag?

I Promise this is a practical guide to Async / Await

With ES8 we got another way to write code that is async in a more readable way then callback's its called Async / Await. With ES6 we already got Promises. To understand Async / Await we first have to understand Promises.

Proxymise Your Async Code

If you've written a fair amount of JavaScript these days, it's likely that you came across promises and their language integration async functions. With Proxymise there is now a way to make your code even more consise!

Asynchronous JavaScript—How Callbacks, Promises, and Async-Await Work

JavaScript touts asynchronous programming as a feature. This means that, if any action takes a while, your program can continue doing other things while the action completes. Once that action is done, you can do something with the result. This turns out the be a great feature for functionality like data fetching, but it can be confusing to newcomers. In JavaScript, we have a few different ways to handle asynchronicity: callback functions, Promises, and async-await.

How to simplify nested async subscriptions in Angular template

One way to subscribe to observable in Angular is async pipe into the HTML template. It is easy but when you have several subscription use ng-container with *ngIf is a common solution, like :

The Async Series: Callbacks

One of the most infamous gotchas in JavaScript to beginners is the idea of asynchronous programming. This series is all about demystifying async in JavaScript.

Vuetify TreeView Async Error (Cannot set property 'vnode' of undefined) Workaround

This is my first blog post here, so I wanted to keep it short and talk about a bug that I came across quite recently in Vuetify TreeView when using Async child loading.

Happy JavaScript Async coding!