Gain insights into JavaScript Promises to handle asynchronous events, chain multiple promises, utilize built-in methods, and master async functions with await expressions for efficient event handling.



js.tar.gz

JS promises

promises

Promises are used to deal with event handling and callbacks in asynchronous programming in JavaScript, such as clicks and key presses. Promises allow developers to specify a function to execute at some later point in response to certain events. Promises may also indicate whether a certain code succeeded or failed in performing its assigned job.

In this course, you will learn how to chain different promises, which makes the code easier to understand and debug. Next, you’ll learn built-in methods to monitor and respond to multiple promises executing in parallel. Then, you will cover async functions and await expressions that are often used with promises. Finally, you’ll learn how to track promises when they are rejected without a rejection handler.

Promises are important to understand and debug the code in asynchronous programming. The concepts of JS promises help developers working with Node.js and Deno for event handling and with asynchronous JavaScript APIs.

JavaScript Promises

# Creating unsettled promises
New promises are created using the `Promise` constructor. This constructor accepts a single argument: a function called the executor, which contains the code to initialize the promise. The executor is passed two functions, `resolve()` and `reject()`, as arguments. When the executor has successfully finished, we call the `resolve()` function  to signal that the promise is resolved, or we call the `reject()` function to indicate that the operation has failed.
Here’s an example using the old `XMLHttpRequest` browser API:

Learn how unsettled promises are created and executor errors are caught.

Introduction

Basics of Promises

Chaining Promises

Working with Multiple Promises

Async Functions and Await Expressions

Tracking Down the Unhandled Rejections

Conclusion

Unsettled Promises

Creating unsettled promises