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

Which method copies the state and value of the previous promise into its returned promise?

Which method copies the state and value of the previous promise into its returned promise?

What is the output of the code below?
```
const promise = Promise.resolve(42+3);

promise.then(value => {
    console.log(value);
    return value + 1;
}).then(value => {
    console.log(value);    
});
console.log(promise);
```

What is the output of the code below?
<pre><code>const promise = Promise.resolve(42+3);

promise.then(value =&gt; {
 console.log(value);
 return value + 1;
}).then(value =&gt; {
 console.log(value); 
});
console.log(promise);
</code></pre>

Is the code below an example of a chained promise?
```
const promise1 = Promise.resolve(42);

const promise2 = promise1.then(value => {
    console.log(value);
});

promise2.then(() => {
    console.log("Finished");
});
```


Is the code below an example of a chained promise?
<pre><code>const promise1 = Promise.resolve(42);

const promise2 = promise1.then(value =&gt; {
 console.log(value);
});

promise2.then(() =&gt; {
 console.log(&quot;Finished&quot;);
});
</code></pre>

Test your knowledge of chaining promises.


Introduction

Basics of Promises

Chaining Promises

Working with Multiple Promises

Async Functions and Await Expressions

Tracking Down the Unhandled Rejections

Conclusion

Quiz: Chaining Promises