There exists a unique syntax that can enhance your performance with promises. It’s async/await: a surprisingly easy and comfortable means to deal with promises. Async functions The async function declaration specifies an asynchronous function, which can return an AsyncFunction object. Async functions perform in a separate order than the rest of the code through the event loop and return a Promise as…

JavaScript promises use the microtask queue for running callbacks. This chapter is dedicated to the exploration of microtasks in JavaScript. Before getting to microtasks it is useful to define JavaScript tasks. A task is considered a JavaScript code that is scheduled to be executed by standard mechanisms. For instance, beginning to run a program, an event callback that…

Promisification is a long term for a straightforward transformation. It represents a conversion of the function, which accepts a callback into a function returning a promise. Often, transformations like that are needed in real-life because multiple libraries and functions are based on callbacks. But, promises are much more convenient. Let’s consider a load_Script(src, callback): Now, we are going to promisify…

As we have already stated, promises in JavaScript represent the eventual completion or failure of an asynchronous operation, as well as its resulting value. The Promise class comprises five static methods. In this chapter, we cover all of them in detail. Promise.all The Promise.all method is used when it is necessary to execute many promises at the same time and wait…

JavaScript promises allow asynchronous code to use structured error handling. The promise chains are served as a great way of error handling. Whenever a promise rejects, the control jumps to the nearest rejection handler. One of the most useful methods of error-handling is .catch. catch As it was already mentioned, .catch is one of the most useful methods for error handling in…

Let’s suppose that you have a sequence of asynchronous tasks to carry out one after another. For example, loading scripts. The JavaScript promises to introduce a couple of receipts to perform that. This chapter is dedicated to promise chaining, which is demonstrated in the example below: The notion is that the result passes through the chain of .then handlers.…

In JavaScript, a promise is a unique object linking the “producing code” and the “consuming code”. In other words, it is a “subscription list”. The “producing code” takes the time it needs to produce the promised result, and the promise makes the result available to the overall subscribed code whenever it’s ready. But, JavaScript promises are more…

Most of the JavaScript actions are asynchronous. To be more precise, you initiate them now, but they finish later. For example, actions like that may be scheduled by setTimeout. For a better understanding, let’s consider the following example: In the case above, you can see the loadScript(src) function loading a script with given src. You can also use the…