Promise.race() and async-await explained in JavaScript?
We will learn about Promise.race() method in this tutorial. As the name of the race() method implies, the promise passed as an argument to the race() method performs a race.
Therefore, no matter which Promise is resolved first, it will only be executed by the race() method, and other Promises will never be executed.
Promise.race()
ThePromise.race method in JavaScript allows you to wait for the first of a set of Promises to be fulfilled or rejected, and handle the result or error that occurs. Once one of the input promises is fulfilled or rejected, it returns a fulfilled or rejected promise, and the value or reason for that promise.
Users can use the promise.race() method according to the following syntax to execute the first settled promise.
Promise.race(iterable).then((response) => {
// handle response
});
In the above syntax, the Promise.race() method takes iterable as the first parameter, and we can handle the response of the successfully executed promise within the "then" block.
Hereiterable Takes an iterable object, such as a set of promises to execute any promise within it, resolved first.
grammar
Here's the syntax for how to use the Promise.race method with async-await in JavaScript:
async function example() {
try {
const result = await Promise.race([promise1, promise2, ...]);
} catch (error) {
// handle error
}
}
Here, promise1, promise2, etc. are the promises you want to wait for. The Promise.race method returns a resolved or rejected Promise containing the value or reason of the first input Promise to be resolved or rejected.
The asynchronous function example uses a try/catch statement to handle error conditions, where if any input promise is rejected, the catch block is executed.
Example 1
In this example, we create multiple Promises and set timers within the Promise to resolve or reject them. We have passed an array of Promise as argument to race() method.
The output shows that the race() method executes a Promise that is rejected because it has no timer. Therefore, the race() method executes the first Promise, which is fulfilled early even if it is rejected or resolved.
<html>
<body>
<h2>Using the Promise.race() </i> Method </h2>
<div id="output"></div>
<script>
let promise_1 = new Promise((res, rej) => {
setTimeout(() => {
res("Resolved promise with time of 0 milliseconds");
}, 1000);
});
let promise_2 = new Promise((res, rej) =>
rej("This promise is rejected!")
);
let promise_3 = new Promise((res, rej) => {
setTimeout(() => {
res("Resolved promise with time of 2000 milliseconds");
}, 2000);
});
Promise.race([promise_1, promise_2, promise_3]).then(
(response) => {
document.getElementById("output").innerHTML +=
"Promise resolved successfully.";
},
(error) => {
document.getElementById("output").innerHTML += "Promise rejected";
}
);
</script>
</body>
</html>
Example 2
In this example, we take a different API and make a promise using the fetch method. We have a series of Promises called requests.
We use the race() method to resolve all requests, no matter which Promise will resolve first, we print the URL in the "then" block.
<html>
<body>
<h2>Using Promise.race() Method with async-await</h2>
<div id = "output"> </div>
<button onclick = "executeRace()"> Fetch data from early promise </button>
<script>
async function executeRace() {
// array of different promises
const requests = [
fetch("https://api.publicapis.org/entries"),
fetch("https://catfact.ninja/fact"),
fetch("https://api.coindesk.com/v1/bpi/currentprice.json"),
];
// resolving the promises using the race() method
const res = await Promise.race(requests);
document.getElementById("output").innerHTML +=
"The first promise resolve is " + res.url;
}
</script>
</body>
</html>
The race() method can be used when the user needs to use the response of the first resolved Promise, even if it is rejected or resolved. If the user needs to use the result of the first successfully resolved Promise, they should use the Promise.any() method.
The above is the detailed content of Promise.race() and async-await explained in JavaScript?. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
1386
52
What should I do if I encounter garbled code printing for front-end thermal paper receipts?
Apr 04, 2025 pm 02:42 PM
Frequently Asked Questions and Solutions for Front-end Thermal Paper Ticket Printing In Front-end Development, Ticket Printing is a common requirement. However, many developers are implementing...
Who gets paid more Python or JavaScript?
Apr 04, 2025 am 12:09 AM
There is no absolute salary for Python and JavaScript developers, depending on skills and industry needs. 1. Python may be paid more in data science and machine learning. 2. JavaScript has great demand in front-end and full-stack development, and its salary is also considerable. 3. Influencing factors include experience, geographical location, company size and specific skills.
How to merge array elements with the same ID into one object using JavaScript?
Apr 04, 2025 pm 05:09 PM
How to merge array elements with the same ID into one object in JavaScript? When processing data, we often encounter the need to have the same ID...
Demystifying JavaScript: What It Does and Why It Matters
Apr 09, 2025 am 12:07 AM
JavaScript is the cornerstone of modern web development, and its main functions include event-driven programming, dynamic content generation and asynchronous programming. 1) Event-driven programming allows web pages to change dynamically according to user operations. 2) Dynamic content generation allows page content to be adjusted according to conditions. 3) Asynchronous programming ensures that the user interface is not blocked. JavaScript is widely used in web interaction, single-page application and server-side development, greatly improving the flexibility of user experience and cross-platform development.
The difference in console.log output result: Why are the two calls different?
Apr 04, 2025 pm 05:12 PM
In-depth discussion of the root causes of the difference in console.log output. This article will analyze the differences in the output results of console.log function in a piece of code and explain the reasons behind it. �...
How to achieve parallax scrolling and element animation effects, like Shiseido's official website?
or:
How can we achieve the animation effect accompanied by page scrolling like Shiseido's official website?
Apr 04, 2025 pm 05:36 PM
Discussion on the realization of parallax scrolling and element animation effects in this article will explore how to achieve similar to Shiseido official website (https://www.shiseido.co.jp/sb/wonderland/)...
Can PowerPoint run JavaScript?
Apr 01, 2025 pm 05:17 PM
JavaScript can be run in PowerPoint, and can be implemented by calling external JavaScript files or embedding HTML files through VBA. 1. To use VBA to call JavaScript files, you need to enable macros and have VBA programming knowledge. 2. Embed HTML files containing JavaScript, which are simple and easy to use but are subject to security restrictions. Advantages include extended functions and flexibility, while disadvantages involve security, compatibility and complexity. In practice, attention should be paid to security, compatibility, performance and user experience.
Is JavaScript hard to learn?
Apr 03, 2025 am 12:20 AM
Learning JavaScript is not difficult, but it is challenging. 1) Understand basic concepts such as variables, data types, functions, etc. 2) Master asynchronous programming and implement it through event loops. 3) Use DOM operations and Promise to handle asynchronous requests. 4) Avoid common mistakes and use debugging techniques. 5) Optimize performance and follow best practices.
