Sending Multiple AJAX Requests at the Same Time – A Comprehensive Guide

Introduction

AJAX (Asynchronous JavaScript and XML) allows web applications to send and receive data from a server asynchronously without reloading the page. In many scenarios, we need to send multiple AJAX requests simultaneously.

For example:

• Fetching data from different APIs at the same time.
• Loading multiple sections of a webpage asynchronously.
• Running multiple background processes concurrently.

This guide provides a detailed explanation of how to send multiple AJAX requests at the same time using different methods, their advantages, handling responses efficiently, and performance optimization techniques.

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Table of Contents

1. Understanding Multiple AJAX Requests
2. Methods to Send Multiple AJAX Requests
3. Using $.ajax() for Multiple Requests
4. Using $.when() and $.Deferred()
5. Using Promise.all() in JavaScript
6. Using fetch() API for Multiple Requests
7. Handling Errors in Multiple Requests
8. Optimizing Performance for Multiple Requests
9. Best Practices for Sending Multiple AJAX Requests
10. Conclusion

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1. Understanding Multiple AJAX Requests

What Happens When You Send Multiple AJAX Requests?

When you send multiple AJAX requests, each request operates independently in an asynchronous manner. However:

• If requests are unrelated, they can execute simultaneously without any issues.
• If requests depend on each other (i.e., one request must finish before another starts), you need to handle them properly using callbacks, promises, or async/await.

Use Cases of Multiple AJAX Requests

• Fetching different datasets (e.g., users, products, categories) simultaneously.
• Running multiple API calls for various page sections.
• Sending multiple form submissions concurrently.
• Handling real-time data updates.

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2. Methods to Send Multiple AJAX Requests

There are multiple ways to send multiple AJAX requests:

1. Using $.ajax() (Traditional jQuery Method)
2. Using $.when() with $.Deferred() (jQuery Promise-based approach)
3. Using Promise.all() (Modern JavaScript Promises)
4. Using fetch() API with Promise.all() (Modern Fetch-based approach)

Each method has its own advantages, which we will discuss in detail.

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3. Using $.ajax() for Multiple Requests

Basic Example

The simplest way to send multiple AJAX requests is by calling $.ajax() multiple times:

$.ajax({
    url: "https://api.example.com/data1",
    type: "GET",
    success: function(response) {
        console.log("Data 1:", response);
    }
});

$.ajax({
    url: "https://api.example.com/data2",
    type: "GET",
    success: function(response) {
        console.log("Data 2:", response);
    }
});

Drawbacks

• Each request is handled independently.
• If the second request depends on the first, we have no control over execution order.
• No built-in error handling for multiple requests.

To handle dependencies, we need to use callbacks (not recommended due to callback hell) or promises.

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4. Using $.when() and $.Deferred()

jQuery provides a better approach to handle multiple AJAX requests using $.when().

Example Using $.when()

$.when(
    $.ajax({ url: "https://api.example.com/data1", type: "GET" }),
    $.ajax({ url: "https://api.example.com/data2", type: "GET" })
).done(function(response1, response2) {
    console.log("Data 1:", response1[0]);
    console.log("Data 2:", response2[0]);
}).fail(function() {
    console.log("One or more requests failed.");
});

Advantages

• Ensures both requests complete before executing .done().
• Can handle success and failure conditions.

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5. Using Promise.all() in JavaScript

For modern JavaScript applications, Promise.all() is a powerful way to handle multiple AJAX requests.

Example Using Promise.all()

const request1 = fetch("https://api.example.com/data1").then(response => response.json());
const request2 = fetch("https://api.example.com/data2").then(response => response.json());

Promise.all([request1, request2])
    .then(([data1, data2]) => {
        console.log("Data 1:", data1);
        console.log("Data 2:", data2);
    })
    .catch(error => {
        console.log("One or more requests failed:", error);
    });

Advantages

• Requests run in parallel.
• .then() executes only after all requests are complete.
• .catch() handles errors in a clean way.

Drawbacks

• If any request fails, Promise.all() rejects the entire operation.

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6. Using fetch() API for Multiple Requests

If you prefer using the fetch() API, you can send multiple requests using async/await.

Example Using async/await

async function fetchData() {
    try {
        let [data1, data2] = await Promise.all([
            fetch("https://api.example.com/data1").then(res => res.json()),
            fetch("https://api.example.com/data2").then(res => res.json())
        ]);

        console.log("Data 1:", data1);
        console.log("Data 2:", data2);
    } catch (error) {
        console.log("One or more requests failed:", error);
    }
}

fetchData();

Advantages

• More readable than chaining .then().
• Can be wrapped in a try-catch block for better error handling.

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7. Handling Errors in Multiple Requests

Error handling is crucial when making multiple AJAX requests.

Using $.when().fail()

$.when(
    $.ajax({ url: "https://api.example.com/data1", type: "GET" }),
    $.ajax({ url: "https://api.example.com/data2", type: "GET" })
).fail(function() {
    console.log("Error occurred while fetching data.");
});

Using Promise.allSettled()

Unlike Promise.all(), Promise.allSettled() completes all requests, even if some fail.

Promise.allSettled([
    fetch("https://api.example.com/data1").then(res => res.json()),
    fetch("https://api.example.com/data2").then(res => res.json())
]).then(results => {
    results.forEach((result, index) => {
        if (result.status === "fulfilled") {
            console.log(`Data ${index + 1}:`, result.value);
        } else {
            console.log(`Request ${index + 1} failed:`, result.reason);
        }
    });
});

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8. Optimizing Performance for Multiple Requests

• Reduce Unnecessary API Calls – Use caching when possible.
• Use Pagination – Fetch large datasets in smaller chunks.
• Batch Requests – Instead of multiple API calls, send a single request that retrieves multiple resources.
• Use WebSockets – For real-time updates instead of polling with AJAX.

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9. Best Practices for Sending Multiple AJAX Requests

• Use Promise.all() or $.when() for better control over multiple requests.
• Implement Error Handling – Use .catch() or try-catch for robust error handling.
• Optimize Requests – Avoid redundant requests to improve performance.
• Use Debouncing – Prevent multiple rapid requests by using a debounce function.
• Monitor Network Performance – Use browser developer tools to track request performance.

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Sending multiple AJAX requests at the same time is a common requirement in modern web applications. This guide covered:

• Basic $.ajax() calls.
• Handling multiple requests with $.when(), Promise.all(), and async/await.
• Error handling strategies.
• Performance optimizations.

Would you like an example integrating these techniques in a real-world project? Let me know!