Promise.all() vs Promise.race()

Asynchronous programming is a fundamental aspect of JavaScript, and promises have emerged as a powerful tool for managing asynchronous operations. Among the various promise functions, Promise.all() and Promise.race() stand out for their ability to handle parallel and competitive asynchronous tasks, respectively. In this article, we will explore the differences between Promise.all() and Promise.race(), providing code examples and code examples to demonstrate their capabilities.

Understanding Promise.all():

Promise.all() allows for the parallel execution of multiple asynchronous operations. It offers several benefits, including:

1. Synchronous Parallel Execution: Promise.all() enables concurrent execution of promises, enhancing performance by avoiding sequential processing.

2. Handling Multiple Promises: By accepting an array of promises, Promise.all() waits for all promises to fulfil or any to reject.

3. Resolving with an Array of Results: The returned promise resolves with an array containing the results of the fulfilled promises, maintaining order according to the input promises.

To illustrate, consider the following code example:

const promise1 = fetch('https://api.example.com/data1');
const promise2 = fetch('https://api.example.com/data2');

Promise.all([promise1, promise2])
  .then(([result1, result2]) => {
    // Process the results
    console.log(result1, result2);
  })
  .catch((error) => {
    // Handle errors
    console.error(error);
  });

Exploring Promise.race():

Promise.race() focuses on competitive asynchronous operations, resolving with the fastest settling promise. Key aspects include:

1. Competitive Asynchronous Operations: Promise.race() determines the outcome based on the first promise to settle, regardless of fulfilment or rejection.

2. Resolving with the Fastest Promise: The returned promise resolves or rejects with the value or rejection reason of the fastest settling promise.

To visualise this, consider the following example:

const promise1 = new Promise((resolve, reject) => {
  setTimeout(resolve, 200, 'Result 1');
});

const promise2 = new Promise((resolve, reject) => {
  setTimeout(resolve, 100, 'Result 2');
});

Promise.race([promise1, promise2])
  .then((result) => {
    console.log(result); // Output: 'Result 2'
  })
  .catch((error) => {
    console.error(error);
  });

Choosing Between Promise.all() and Promise.race():

To decide between Promise.all() and Promise.race(), consider the following factors:

1. Nature of Operations: Use Promise.all() for parallel execution of multiple promises, while Promise.race() is ideal for competitive scenarios where the fastest result matters.

2. Handling Results: Promise.all() provides an array of results, allowing further processing or aggregation, whereas Promise.race() returns the result of the fastest promise, which may be sufficient in some cases.

By carefully assessing your use case and requirements, you can choose the appropriate function to achieve the desired outcome.

Comments

[websilvercraft]

Here is my practical example of Promise.race to add timeouts to fetch calls. I use it in production to make sure the calls don't remain hanged up to consume server's resources.