JavaScript promises helps us to handle asynchronous operations more efficiently by assigning the handler with the success value or failure reason.

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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

In the first generation of promises, a rejected promise without a rejection handler would silently fail. Many considered this the biggest flaw in the specification because it was the only part of the JavaScript language that didn’t make errors apparent. Later, JavaScript runtimes instituted console warnings to at least notify developers when unhandled rejections occurred, and some runtime environments decided to throw errors. Eventually, unhandled rejection tracking was added to the JavaScript specification.

## Handling promise rejection
Determining whether a promise rejection was handled isn’t straightforward due to the nature of promises. For instance, consider this example:

In the first generation of promises, a rejected promise without a rejection handler would silently fail. Many considered this the biggest flaw in the specification because it was the only part of the JavaScript language that didn’t make errors apparent. Later, JavaScript runtimes instituted console warnings to at least notify developers when unhandled rejections occurred, and some runtime environments decided to throw errors. Eventually, unhandled rejection tracking was added to the JavaScript specification.

# Handling promise rejection
Determining whether a promise rejection was handled isn’t straightforward due to the nature of promises. For instance, consider this example:

Learn how to detect unhandled rejections and how a web browser tracks them.

Introduction

Basics of Promises

Chaining Promises

Working with Multiple Promises

Async Functions and Await Expressions

Tracking Down the Unhandled Rejections

Conclusion

How to Detect an Unhandled Rejection

Handling promise rejection