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

## Using the `for-await-of` loop
Another special syntax enabled inside async functions is the `for-await-of` loop, which allows us to retrieve values from an iterable or an async iterable. An **iterable** is an object with a `Symbol.iterator` method that returns an iterator. An **async iterable** is an object with a `Symbol.asyncIterator` method that returns an iterator whose values are always promises. The `for-await-of` loop calls `Promise.resolve()` on each value returned from an iterable and then waits for each promise to resolve before continuing to the next iteration of the loop.

The most often used iterables in JavaScript are arrays, and we can use an array of promises with a `for-await-of` loop to process promises in sequence, like in this example:

# Using the `for-await-of` loop
Another special syntax enabled inside async functions is the `for-await-of` loop, which allows us to retrieve values from an iterable or an async iterable. An **iterable** is an object with a `Symbol.iterator` method that returns an iterator. An **async iterable** is an object with a `Symbol.asyncIterator` method that returns an iterator whose values are always promises. The `for-await-of` loop calls `Promise.resolve()` on each value returned from an iterable and then waits for each promise to resolve before continuing to the next iteration of the loop.

The most often used iterables in JavaScript are arrays, and we can use an array of promises with a `for-await-of` loop to process promises in sequence, like in this example:

Learn how the for-await-of loop is used to iterate over every promise.

Introduction

Basics of Promises

Chaining Promises

Working with Multiple Promises

Async Functions and Await Expressions

Tracking Down the Unhandled Rejections

Conclusion

Await Expressions and Loops

Using the `for-await-of` loop