How do I save XMLHttpRequest.responseText in a variable

Question

The code below keeps returning undefined

        
    console.log("Get users...");
        xhr = getXmlHttpRequestObject();
        xhr.onreadystatechange = dataCallback;
        // asynchronous requests
        
        const data = xhr.open("GET", "http://localhost:6868/content", true);
        console.log(data);
        }