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 also accepts an iterable of promises and returns a fulfilled promise when any of the passed-in promises are fulfilled?


Which method also accepts an iterable of promises and returns a fulfilled promise when any of the passed-in promises are fulfilled?

Which method monitors and returns a promise that is resolved only when every promise in the iterable is resolved?

Which method monitors and returns a promise that is resolved only when every promise in the iterable is resolved?

`[{ status: ‘_fulfilled_’ },`
  
`{ status: ‘_fulfilled_’ }]`

`[{ value: ‘_Promise1 is resolved_’ },`
  
`{ value: ‘_Promise2 is resolved_’ }]`

`[{ status: ‘_fulfilled_’, value: ‘_Promise1 is resolved_’ },`
  
`{ status: ‘_fulfilled_’, value: ‘_Promise2 is resolved_’ }]`

`[{ ‘_Promise1 is resolved_’ }, { ‘_Promise2 is resolved_’ }]`

What is the output of the code below?
```
let promise1 = new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve(43);
    }, 100);
});
let promise2 = new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve(44);
    }, 100);
});
let result = Promise.allSettled([promise1, promise2]);
result.then((data) => console.log(data));
```

What is the output of the code below?
<pre><code>let promise1 = new Promise((resolve, reject) =&gt; {
 setTimeout(() =&gt; {
 resolve(43);
 }, 100);
});
let promise2 = new Promise((resolve, reject) =&gt; {
 setTimeout(() =&gt; {
 resolve(44);
 }, 100);
});
let result = Promise.allSettled([promise1, promise2]);
result.then((data) =&gt; console.log(data));
</code></pre>

What is the output of the code below?
```
let promise1 = new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve(43);
    }, 100);
});
let promise2 = new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve(44);
    }, 100);
});
let promise3 = Promise.race([promise1, promise2]);
promise3.then(value => console.log(value));
```

What is the output of the code below?
<pre><code>let promise1 = new Promise((resolve, reject) =&gt; {
 setTimeout(() =&gt; {
 resolve(43);
 }, 100);
});
let promise2 = new Promise((resolve, reject) =&gt; {
 setTimeout(() =&gt; {
 resolve(44);
 }, 100);
});
let promise3 = Promise.race([promise1, promise2]);
promise3.then(value =&gt; console.log(value));
</code></pre>

**(True or False)** The returned promise of the `Promise.allSettled()` method is never rejected.

(True or False) The returned promise of the <code>Promise.allSettled()</code> method is never rejected.

Test your knowledge of working with multiple promises.


Introduction

Basics of Promises

Chaining Promises

Working with Multiple Promises

Async Functions and Await Expressions

Tracking Down the Unhandled Rejections

Conclusion

Quiz: Working with Multiple Promises