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Batch and Sequential Endpoint Requests in JavaScript

by | Jun 25, 2023

Batch Endpoint Requests

To call an endpoint multiple times with an array of IDs in JavaScript, you can use a loop or an asynchronous operation like Promise.all to make the requests all at once. Here’s an example:

const ids = [1, 2, 3, 4, 5];

// Calling the endpoints all at once
const requests = ids.map(id => fetch(`https://api.example.com/endpoint/${id}`));

Promise.all(requests)
  .then(responses => {
    // Handle the responses here
    responses.forEach(response => {
      // Process each response
    });
  })
  .catch(error => {
    // Handle any errors that occurred
  });

In this example, we have an array of IDs (ids). We use the map function to create an array of promises, where each promise represents a request to the endpoint with a specific ID. Then, we use Promise.all to wait for all the promises to resolve. Once all the requests are completed, the .then block is executed, where you can handle the responses individually.

Promises are a fundamental concept that simplifies the handling of asynchronous operations.

Understanding Promises in JavaScript

Before we delve into Promise.all(), let’s have a quick refresher on promises. Promises are objects that represent the eventual completion or failure of an asynchronous operation. They provide a cleaner and more organized way to handle asynchronous tasks compared to callbacks.

The Promise.all() Method

Promise.all() is a built-in method in JavaScript that allows you to deal with multiple promises concurrently. It takes an iterable of promises as an input and returns a new promise that fulfills when all of the input promises have fulfilled, or rejects when any of them has been rejected.

How Promise.all() Works

When you call Promise.all(), it waits for all the promises in the iterable to complete. If all promises fulfill successfully, the returned promise from Promise.all() fulfills with an array of their values in the same order. However, if any of the input promises is rejected, the returned promise rejects with the reason of the first promise that was rejected.

Use Cases for Promise.all()

  • Data Fetching: When you need to fetch data from multiple sources and only proceed when all the data is available.
  • Parallel Processing: For performing multiple operations concurrently, such as image loading or API calls.
  • Batch Operations: Useful for sending multiple requests to a server and waiting for all responses.

Advantages of Promise.all()

  • Efficiency: It improves the efficiency of asynchronous operations by running tasks concurrently.
  • Clean Code: Makes the code cleaner and more readable compared to nesting callbacks.
  • Error Handling: It simplifies error handling by allowing you to catch errors in one place.

Handling Errors with Promise.all()

To handle errors with Promise.all(), you can use a .catch() block after calling the method to capture any potential rejections within the array of promises. This ensures that the overall promise doesn’t fail prematurely.

Promise.allSettled() vs. Promise.all()

While Promise.all() rejects if any of the input promises is rejected, Promise.allSettled() waits for all promises to settle, whether they fulfill or reject. It returns an array with the status and result of each promise, making it useful for scenarios where you want to know the outcome of all promises, regardless of success or failure.

Implementing Promise.all() in Your Code

To implement Promise.all(), first create an array of promises, and then pass this array as an argument to the Promise.all() method. You can then use .then() and .catch() to handle the combined promise.

Best Practices for Using Promise.all()

  • Ensure that all promises in the iterable have a proper error-handling mechanism.
  • Consider the order of promises in the iterable when using the results.
  • Use Promise.allSettled() if you need to know the status of every promise.

Sequential Endpoint Requests

If you want to call the endpoints one by one, you can use a loop or recursion along with asynchronous operations like async/await or fetch. Here’s an example:

const ids = [1, 2, 3, 4, 5];

// Calling the endpoints one by one
async function callEndpoints() {
  for (let i = 0; i < ids.length; i++) {
    try {
      const response = await fetch(`https://api.example.com/endpoint/${ids[i]}`);
      // Process the response here
    } catch (error) {
      // Handle any errors that occurred
    }
  }
}

// Call the function
callEndpoints();

In this example, the callEndpoints function is defined as an async function, allowing the use of await inside the loop. The loop iterates through each ID in the ids array, and for each iteration, an asynchronous request is made using fetch. The await keyword ensures that each request is completed before moving on to the next iteration.

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