Learn how to use these two features. An async constructor would pseudo-logic be what @dalu wrote: The code quickly becomes … Take your JavaScript skills to the next level! No callback nesting or .then() chaining needed. Find out how to return the result of an asynchronous function, promise based or callback based, using JavaScript Published Sep 09, 2019 , Last Updated Apr 30, 2020 Say you have this problem: you are making an asynchronous call, and you need the result of that call to be returned from the original function. Async functions and async methods always return a Promise, either resolved or rejected. Promises are great for writing asynchronous code and have solved the famous callback hell problem as well, but they also introduced their own complexities. Asynchronous JavaScript: Asynchronous code allows the program to be executed immediately where the synchronous code will block further execution of the remaining code until it finishes the current one. They are built on top of promises and allow us to write asynchronous code in synchronous manners.. Why Async/await? This may not look like a big problem but when you see it in a bigger picture you realize that it may lead to delaying the User Interface. With ES6 classes, writing object-oriented JavaScript is easier then ever before. Stores class methods, such as sayHi, in User.prototype. Now that our methods are marked as being asynchronous, we can tell our code to await for them to finish before proceeding. Whats is async. class AFactory {static async create {return new A (await Promise. resolve ('fooval'));}} This only makes the params to the constructor to be async , not the constructor itself. await keyword before a promise makes JavaScript wait until that is resolved/rejected. You must attach then() and catch(), no matter what. Async functions and async methods do not throw errors in the strict sense. The Async statement is to create async method in JavaScript.The function async is always return a promise.That promise is rejected in the case of uncaught exceptions, otherwise resolved to the return value of the async function. ES6 classes and async/await are among the most important new features in JavaScript. The same is true about writing asynchronous JavaScript, thanks to async/await. How to Throw Errors From Async Functions in JavaScript: catch me if you can. The function code is taken from the constructor method (assumed empty if we don’t write such method). After new User object is created, when we call its method, it’s taken from the prototype, just as described in the chapter F.prototype. async keyword makes a method asynchronous, which in turn always returns a promise and allows await to be used. async function fn() {return 'hello';} fn().then(console.log) // hello. The new methods array. let cheese = new Cheese(); let dough = new Dough(); let pizza = await Pizza.create(cheese, dough); console.log(pizza); There is only one more thing we’re missing. Looking to become fluent in async/await? Whats Await in JavaScript Because we have used async, the return value 'hello' is wrapped in a promise (via Promise constructor). async function asyncFunc {return "Hey!". To create an async function all we need to do is add the async keyword before the function definition, like this:. The run() function shouldn't be responsible for handling every possible error, you should instead do run().catch(handleError). The async property will be a boolean that tells us whether the function is asynchronous and the func property is the function that we want to execute. (Or wrap the method inside try/catch). The function fn returns 'hello'. So the object has access to class methods. async function always returns a promise. 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