Efficient AJAX Handling in jQuery: Custom Wrapper for Aborting, Error Management & Race condition

Optimizing AJAX Requests with a Custom Wrapper in jQuery

Table of Contents

1. Introduction
   • Avoid Race Conditions
   • Lazy vs Eager Approach
2. Approach 1: Cancelling Only Duplicate Requests
   • 1 Core Concept
   • 1 Code Implementation
3. Approach 2: Cancelling All Active Requests
   • 2 Core Concept
   • 2 Code Implementation
4. Approach 3: Handling Only the Latest Response
   • 3 Core Concept
   • 3 Code Implementation
5. Comparison of Approaches
6. Pros and Cons of Adding a Wrapper in jQuery AJAX
   • Pros
   • Cons
7. Choosing the Right Approach
8. Final Thoughts
9. Conclusion

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Introduction

In modern web applications, efficient network communication is crucial for performance and user experience. One common issue arises when multiple duplicate API requests are triggered, leading to unnecessary network traffic and potential data inconsistencies. To mitigate this, we can implement a custom AJAX wrapper in jQuery. This article explores three approaches:

1. Cancelling Only Duplicate Requests: Tracks active requests and cancels duplicate API calls.
2. Cancelling All Active Requests: Cancels all ongoing AJAX requests before initiating a new one.
3. Handling Only the Latest Response: Processes only the latest response while ignoring older ones.

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Avoid Race Conditions

One of the primary motivations for implementing a custom AJAX wrapper is to avoid race conditions in the code. Race conditions occur when multiple asynchronous requests are initiated simultaneously, and their responses arrive out of order, leading to inconsistent or incorrect data being displayed in the UI. For example, if a user rapidly clicks a button that triggers multiple API calls, the responses might not return in the same order they were sent, causing the UI to reflect outdated or incorrect information. By canceling duplicate requests, aborting all active requests, or processing only the latest response, we can ensure that the application handles data in a predictable and consistent manner, effectively mitigating race conditions.

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Lazy vs Eager Approach

When optimizing AJAX requests, you can adopt either a lazy or eager approach. A lazy approach focuses on minimizing redundant requests by canceling duplicates or ignoring outdated responses. On the other hand, an eager approach aggressively cancels all active requests to ensure only the latest request is processed. The choice depends on your application's requirements and the nature of the API calls.

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Approach 1: Cancelling Only Duplicate Requests

1 Core Concept

• Each API request is assigned a unique ID based on the URL and method.
• Active requests are stored in a Map.
• When a duplicate request is detected, the previous one is aborted.
• Requests are removed from tracking once completed.

1 Code Implementation

// Map to store active XHR requests
var x_activeXHRsMap = new Map();

// Function to override jQuery's AJAX method
function overrideAjaxCalls($, utils) {
  var originalAjax = $.ajax;

  $.ajax = function (options) {
    // Skip non-relevant API calls
    if (!utils.isIrServicePath(options.url)) {
      return originalAjax.call($, options);
    }

    // Generate a unique request ID based on URL and method
    const requestId = utils.generateRequestId(options.url, options.method || "GET");

    // Check if a duplicate request is already in progress
    if (x_activeXHRsMap.has(requestId)) {
      const existingXHR = x_activeXHRsMap.get(requestId);
      if (existingXHR && existingXHR.readyState !== 4) {
        existingXHR.abort(); // Abort the duplicate request
        console.log(`Aborted duplicate API call: ${options.url}`);
      }
    }

    // Initiate the new request
    let xhr = originalAjax.call($, options);
    x_activeXHRsMap.set(requestId, xhr); // Track the new request

    // Clean up the request from the map once it completes
    xhr.always(() => {
      x_activeXHRsMap.delete(requestId);
    });

    return xhr;
  };
}

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Approach 2: Cancelling All Active Requests

2 Core Concept

• Cancels all ongoing AJAX requests before initiating a new one.
• Useful when clicking a button triggers multiple requests in quick succession.

2 Code Implementation

// Array to store active XHR requests
var activeXHRs = [];

// Function to override jQuery's AJAX method
function overrideAjaxCalls($) {
  var originalAjax = $.ajax;

  $.ajax = function (options) {
    // Abort all active XHR requests before starting a new one
    activeXHRs.forEach(xhr => xhr.abort());
    activeXHRs = []; // Clear the array

    // Initiate the new request
    let xhr = originalAjax.call($, options);
    let originalFailHandlers = [];

    // Handle failed requests
    xhr.fail((xhrObj, status, error) => {
      if (status === "abort") {
        console.warn(`Request aborted: ${options.url}`);
      } else {
        originalFailHandlers.forEach((fn) => fn.apply(this, [xhrObj, status, error]));
      }
    });

    // Override the fail method to capture custom handlers
    xhr.fail = function (callback) {
      if (typeof callback === "function") {
        originalFailHandlers.push(callback);
      }
      return this;
    };

    // Track the new request
    activeXHRs.push(xhr);

    // Clean up the request from the array once it completes
    xhr.always(() => {
      activeXHRs = activeXHRs.filter(activeXhr => activeXhr !== xhr);
    });

    return xhr;
  };
}

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Approach 3: Handling Only the Latest Response

3 Core Concept

• Does not abort previous requests but only processes the latest response.
• Uses a versioning mechanism to ignore outdated responses.

3 Code Implementation

// Global variable to track the latest request version
var x__XHRVersion = 0;

// Function to override jQuery's AJAX method
function overrideAjaxCalls($, utils) {
  var originalAjax = $.ajax;

  $.ajax = function (options) {
    // Skip non-relevant API calls
    if (!utils.isIrServicePath(options.url)) {
      return originalAjax.call($, options);
    }

    // Increment the version for the new request
    let x__currentXHRVersion = ++x__XHRVersion;
    let xhr = originalAjax.call($, options);

    // Process only the latest response
    xhr.then(
      function (data, textStatus, jqXHR) {
        if (x__currentXHRVersion === x__XHRVersion) {
          console.log("Processing latest response: ", options.url);
        }
      },
      function (jqXHR, textStatus, errorThrown) {
        if (x__currentXHRVersion === x__XHRVersion) {
          console.warn("Handling error response: ", options.url);
        }
      }
    );

    return xhr;
  };
}

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Comparison of Approaches

Feature	Cancelling Duplicate Requests	Cancelling All Requests	Handling Only Latest Response
Use Case	Avoid duplicate API calls	Cancel all requests before new one	Ensure only the latest response is processed
Request Tracking	Tracks using unique request ID	No tracking, just abort all	Uses versioning for response management
Best For	APIs with heavy traffic	UI events triggering rapid API calls	Ensuring UI reflects only the most recent data

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Pros and Cons of Adding a Wrapper in jQuery AJAX

Pros

• Improves performance by reducing redundant API calls.
• Enhances user experience by avoiding unnecessary delays.
• Provides better resource management and automatic cleanup.
• Offers more control over API calls.
• Prevents UI flickering and inconsistent states.

Cons

• Approach 2 may cancel important requests.
• Requires additional tracking logic, adding some complexity.
• Debugging aborted requests can be more difficult.
• Might interfere with WebSocket or long-polling requests.

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Choosing the Right Approach

Feature	Approach 1	Approach 2	Approach 3
Efficiency	High	Medium	High
Control	Fine-grained	Aggressive	Moderate
Best For	Avoiding duplicates	UI-triggered frequent API calls	Processing only the latest response

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Final Thoughts

• Approach 1 (Cancelling Only Duplicate Requests) is best for APIs that experience duplicate calls.
• Approach 2 (Cancelling All Requests) is useful when UI actions trigger multiple requests rapidly.
• Approach 3 (Handling Only Latest Response) is ideal when only the most recent response should be used.

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Conclusion

By implementing these strategies, developers can optimize network usage, improve performance, and enhance user experience in web applications. Each approach has its strengths and trade-offs, so choose the one that aligns best with your application's requirements. Whether you need to cancel duplicates, abort all requests, or process only the latest response, a custom AJAX wrapper in jQuery can help you achieve your goals efficiently.