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.



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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

# Using `await` expressions
The `await` expressions are designed to make working with promises simpler. Instead of manually assigning fulfillment and rejection handlers, any promise used in an `await` expression behaves more like code in a synchronous function. The expression returns the fulfilled value of a promise when it succeeds and throws the rejection value when the promise fails. This allows us to easily assign the result of an `await` expression to a variable and catch any rejections using a `try-catch` statement. Here’s an example of using the `fetch()` API without `await`:

The `retrieveJsonData()` function returns a promise that resolves to the JSON data in the response from the call to `fetch()`. 
# Fetching data with `await`
There is also a rejection handler to print out any error messages. Here’s how we can rewrite this function as an async function that uses `await`:


Learn how await expressions assign the value of a promise to a variable and catch rejections.

Introduction

Basics of Promises

Chaining Promises

Working with Multiple Promises

Async Functions and Await Expressions

Tracking Down the Unhandled Rejections

Conclusion

Await Expressions

Using `await` expressions

Await Expressions

Using await expressions

Using `await` expressions