How can I intercept AJAX requests on a web page for custom actions?

How to Hook into AJAX Requests on a Web Page

Intercepting AJAX requests on a web page allows developers to perform custom actions before sending requests or process responses from the server. This can be useful for logging, modifying requests, or enhancing security.

Using Event Listeners

One approach to hook into AJAX requests is to use event listeners. By attaching an event listener to the XMLHttpRequest object, developers can capture events such as "load" and "readystatechange" and perform actions based on the request status. The following code snippet demonstrates how to add an event listener to monitor all AJAX requests:

(function() {
    var origOpen = XMLHttpRequest.prototype.open;
    XMLHttpRequest.prototype.open = function() {
        console.log('request started!');
        this.addEventListener('load', function() {
            console.log('request completed!');
            console.log(this.readyState); //will always be 4 (ajax is completed successfully)
            console.log(this.responseText); //whatever the response was
        });
        origOpen.apply(this, arguments);
    };
})();

In this code, the open() method of the XMLHttpRequest prototype is overridden to attach a load event listener to each request. When an AJAX request is initiated, the load event will be triggered, and the specified callback function will be executed.

By using event listeners, developers can perform various actions based on the event type. For example, they can log the request details, modify the request headers, or process the response data.

Compatibility Notes

The event listener approach is supported by most modern browsers, including Chrome, Firefox, and Edge. However, it may not work correctly in older versions of Internet Explorer (IE), and it does not support native fetch API requests.

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