In the world of web development, JavaScript has become an essential tool. One of the key features that makes it an excellent choice for developers is its Promise functionality.
Promises are objects that allow for asynchronous programming in JavaScript, which means that code that is waiting for certain events to occur can run simultaneously. One specific method of the Promise API is Promise.any(), and it is particularly useful when dealing with multiple promises in parallel.
This article will explore the Promise.any() method’s functionality, using examples to explain how it works in different scenarios. Description of Promise.any() method
The Promise.any() method takes an array of promises as its argument and returns a new promise that is resolved as soon as one of the promises in the array is fulfilled.
The returned promise will have the same value as the first fulfilled promise. If all the promises in the array are rejected, the returned promise is rejected as well.
One notable aspect of the Promise.any() method is that it doesn’t wait for all promises to complete like the Promise.all() method. Instead, it waits until the first promise is fulfilled or rejected.
Illustration of the method’s functionality
When the Promise.any() method is used, it listens for any promise among the array to be fulfilled. If any promise is fulfilled, the returned promise resolves with its value.
If no promises are fulfilled, and all promises in the array are rejected, the returned promise is rejected. If the returned promise is rejected, an error message called AggregateError is thrown.
AggregateError is a subclass of the Error object, and it contains an array of individual rejection errors as its parameter. JavaScript Promise.any() examples
Example 1: All promises fulfilled
In this example, we have an array of promises that need to be resolved by the Promise.any() method.
When all the promises fulfill, the Promise.any() method returns the value of the first fulfilled promise. Here is a sample code snippet:
“`javascript
const promises = [Promise.resolve(1), Promise.resolve(2), Promise.resolve(3)];
Promise.any(promises).then((result) => {
console.log(result); // Output: 1
});
“`
Example 2: One promise rejected
When one of the promises in the array is rejected, Promise.any() method returns the value of the first fulfilled promise:
“`javascript
const promises = [Promise.resolve(1), Promise.reject(2), Promise.resolve(3)];
Promise.any(promises)
.then((result) => {
console.log(result);
})
.catch((error) => {
console.log(error); // Output: Error: Promise.any() all promises were rejected
});
“`
Here, since the second promise is rejected, the returned promise is fulfilled with the value of the first fulfilled promise (1).
However, the catch block is executed because the Promise.any() method detects that a promise in the array has been rejected. Example 3: All promises rejected
In this example, we have an array of promises that are all rejected, and the Promise.any() method returns an AggregateError:
“`javascript
const promises = [Promise.reject(1), Promise.reject(2), Promise.reject(3)];
Promise.any(promises)
.then((result) => {
console.log(result);
})
.catch((error) => {
console.log(error.errors); // Output: [1, 2, 3]
});
“`
In this case, since all promises in the array are rejected, the returned promise is also rejected.
An AggregateError is thrown, which contains the array of individual rejection errors.
Conclusion
In this article, we have learned about the Promise.any() method and how it works with different types of promises. We discovered that Promise.any() listens for any promise among an array to be fulfilled and resolves with its value, or it will reject if all promises in the array are rejected.
Furthermore, we shared three examples, including when all promises fulfill, when a single promise is rejected, and when all promises are rejected. In conclusion, Promise.any() is a useful tool when working with multiple promises in parallel that should not wait for all Promises to complete.
When to use the JavaScript Promise.any() method
The Promise.any() method can be used in several situations where you want to fetch data from multiple sources, and you only need the first one to resolve. One scenario that is increasingly common is content delivery networks (CDN) for websites.
Use case for Promise.any() method
CDNs are third-party servers that store website content (images, videos, JavaScript files, etc.) and provide faster, more efficient loading times by reducing the load on the user’s server. CDNs often store multiple versions of the same content in different locations worldwide to ensure that content is delivered from the server closest to the user, which improves the loading times even further.
When working with multiple servers, you can use Promise.any() method to quickly load content from whichever server responds first and keep the user waiting for the rest of the servers to reply. Example of using Promise.any() method to fetch images from multiple URLs
Another example of using Promise.any() with the fetch API is the fetching of images from multiple URLs. Sometimes it’s better to use the Promise.any() method to load images from a variety of URLs because you don’t want the loading of images to stop if one URL is down or slow.
The Promise.any() method will resolve with the first URL that has the image, so it will load the image quickly, instead of waiting for every URL to respond before displaying the image. Here is an example of how to use Promise.any() to load an image from a list of URLs:
“`javascript
const urls = [
“https://example.com/image1”,
“https://example.com/image2”,
“https://example.com/image3”
];
let data;
Promise.any(
urls.map(url => fetch(url).then(response => {
if (response.ok){
return response.blob();
}
throw new Error(‘Network response was not ok.’);
}).then(blob => {
data = blob;
}))
)
.then(() => {
const img = document.createElement(‘img’);
img.src = URL.createObjectURL(data);
document.body.appendChild(img);
})
.catch(() => console.log(‘All URLs have failed’));
“`
In this example, we passed an array of URLs to Promise.any(), which we created to fetch the images from each URL.
As soon as the first URL returns the image data, Promise.any() will resolve with that result. The Promise.any() method will also catch an error if all of the URLs are unable to return an image.
Summary
In summary, the Promise.any() method is an excellent tool when working with multiple promises in parallel that should execute independently of each other. Promise.any() works by listening for the first promise to resolve, and then it returns the result.
This method is significant in scenarios where you want to quickly extract data from a list of URLs or load content from a variety of locations, with the added benefit of not having to wait for all promises to complete. The use of Promise.any() can help improve website loading times and increase the overall user experience.
In conclusion, the Promise.any() method is an essential tool in JavaScript for handling multiple promises in parallel. It allows for the quick delivery of content, such as images from various sources like content delivery networks (CDNs).
The method is incredibly efficient, and it does not require waiting for all promises to complete before proceeding, making it a practical solution for web developers. By using the Promise.any() method, website loading times can be significantly reduced, providing an overall better user experience.
Web developers can take advantage of this powerful tool to improve the performance of their websites, and the examples provided in this article serve as guides to this end.