Using Callback Functions to Retrieve Asynchronous HTTP Request Results in Node.js Microservices

The author documents a problem encountered while refactoring a monolithic application into several microservices, where internal data exchange turned into inter‑service HTTP communication.

To handle the communication, a Node.js core module wrapper for an HTTP request was created; the diagram below shows three parameters being sent to a backend service and the response being returned.

The issue arises because the HTTP request is asynchronous: the variable returned at the end of the function is undefined since the callback that receives the response has not executed yet.

The solution is to add a callback function as a parameter. Inside the http.request response handler, the callback is invoked with null for the error argument (or an error object if one occurs) and the obtained result. This allows the caller to receive the data once the asynchronous operation completes.

The custom callback function is exported, and its usage is illustrated in the following diagram, showing how to import the module and call the function with a callback to obtain the response data.

By applying this callback pattern, the asynchronous HTTP request’s result can be accessed reliably, providing a clearer understanding of callbacks in Node.js, even if the microservice example was a tongue‑in‑cheek demonstration.