How to Intercept All AJAX Requests on a Page with Custom Actions?

Intercepting All AJAX Requests on a Page with Custom Actions

Q: Is it possible to "hook" into all AJAX requests on a page, either before they're sent or during events, to perform custom actions?

A: Yes, it's possible with the following approach:

Intercepting AJAX Requests

To intercept all AJAX requests on a page, we can override the open() method of the XMLHttpRequest object, which is used to initiate the requests. By intercepting the open() method, we can execute our custom actions before the request is sent.

Here's the code to intercept AJAX requests:

<code class="js">(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);
    };
})();</code>

By executing the above code, we can perform any necessary actions, such as logging the request URL, adding additional headers, or modifying the request data.

Third-Party Scripts

This approach works even with third-party scripts using jQuery or other AJAX libraries because we're intercepting the underlying XMLHttpRequest object, which is used by all AJAX implementations. However, it's important to note that this approach may not work with native fetch API.

Additional Resources

For more information on the addEventListener API for handling AJAX events, refer to: https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Using_XMLHttpRequest#Monitoring_progress

Browser Support

This approach does not work for Internet Explorer 8 or earlier.

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