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

Async functions are different from synchronous functions in four ways:
* The return value is always a promise. 
* Thrown errors are promise rejections. 
* The `await` expression can be used.
* The `for-await-of` loop can be used.

These four aspects of async functions make them quite different from synchronous ones, so it’s worth going through each point in more detail.

## The return value is always a promise
We can use the `return` operator in async functions the same way as in synchronous functions. The difference is that async functions always return a promise, regardless of the type of value we specify with `return`. If we return a number, for example, that number is wrapped in a promise:

Async functions are different from synchronous functions in four ways:
* The return value is always a promise. 
* Thrown errors are promise rejections. 
* The `await` expression can be used.
* The `for-await-of` loop can be used.

These four aspects of async functions make them quite different from synchronous ones, so it’s worth going through each point in more detail.

# The return value is always a promise
We can use the `return` operator in async functions the same way as in synchronous functions. The difference is that async functions always return a promise, regardless of the type of value we specify with `return`. If we return a number, for example, that number is wrapped in a promise:

Distinguish between asynchronous and synchronous functions.

Introduction

Basics of Promises

Chaining Promises

Working with Multiple Promises

Async Functions and Await Expressions

Tracking Down the Unhandled Rejections

Conclusion

What Makes Async Functions Different?

The return value is always a promise