Javascript wait for result of async function
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JavaScript is a bit like The Faceless Men of the programming world.It can be Asynchronous. It can be Functional. It can be Object-oriented. It can be Client-side. It can be Server-side. The list goes on. This article will focus on Asynchronous JavaScript. But wait, JavaScript is a synchronous language!This means only one operation can be carried out at a time. But that’s not the entire picture here. There are many ways JavaScript provides us with the ability to make it behave like an asynchronous language. One of them is with the Async-Await clause. What is async-await?Async and Await are extensions of promises. If you are not clear with the concepts of Promise, you can refer my previous post How to write Promises in JavaScript. AsyncAsync functions enable us to write promise based code as if it were synchronous, but without blocking the execution thread. It operates asynchronously via the event-loop. Async functions will always return a value. Using async function firstAsync() { Running the above code gives the alert output as 27, it means that a AwaitThe await operator is used to wait for a Promise. It can be used inside an Async block only. The keyword Await makes JavaScript wait until the promise returns a result. It has to be noted that it only makes the The code block below shows the use of Async Await together. async function firstAsync() { Things to remember when using Async AwaitWe can’t use the await keyword inside of regular functions.function firstAsync() { To make the above function work properly, we need to add Async Await makes execution sequentialNot necessarily a bad thing, but having paralleled execution is much much faster. For example: async function sequence() { The above takes 100ms to complete, not a huge amount of time but still slow. This is because it is happening in sequence. Two promises are returned, both of which takes 50ms to complete. The second promise executes only after the first promise is resolved. This is not a good practice, as large requests can be very time consuming. We have to make the execution parallel. That can be achieved by using
According to MDN:
Promise.all()async function sequence() { The Another method: async function parallel() { // Start a 500ms timer asynchronously… Async Await is very powerful but they come with caveats. But if we use them properly, they help to make our code very readable and efficient. I hope you have learned something new! If you found this article useful, be sure to share, follow and support! More content at PlainEnglish.io. Sign up for our free weekly newsletter. Follow us on Twitter, LinkedInand Discord.
Does JavaScript wait for async function to finish?JavaScript code execution is asynchronous by default, which means that JavaScript won't wait for a function to finish before executing the code below it.
Can you return from an async function?Async functions always return a promise. If the return value of an async function is not explicitly a promise, it will be implicitly wrapped in a promise. Note: Even though the return value of an async function behaves as if it's wrapped in a Promise.resolve , they are not equivalent.
Does async await wait?The await operator is used to wait for a Promise . It can only be used inside an async function within regular JavaScript code; however it can be used on its own with JavaScript modules.
Does await block JavaScript?If you execute the above program, you will get to know, await only makes sure an async block waits. It does not stop JavaScript from executing other operations.
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