Javascript HTTP data stream reset response

Question

I've been having a hard time writing websockets in PHP, so I decided to try to download a datastream. It works, I can get content in different times, parse it, and use it, but the entire response is saved into memory...

Is there a way to reset the request's response every time in onreadystatechange function? (where that comment is)

Removing the comment, I get this error:

test.html:20 Uncaught TypeError: Cannot assign to read only property 'responseText' of object '#'

A working code for streaming:

class HTTPStream {
    constructor(url, callback, error) {
        this.request = new XMLHttpRequest();

        var previous_text = '';

        if (typeof error === "function")
            this.request.onerror = error;

        this.request.onreadystatechange = () => {
            if (this.request.readyState > 2) {
                var new_response = this.request.responseText.substring(previous_text.length);
                if(new_response != "") {
                    var result = JSON.parse(new_response);
                    callback(result);
                }
                previous_text = this.request.responseText;
                //this.request.responseText = "";
            }
        };
        this.request.open("GET", url, true);
        this.request.send();
    }

    cancel() {
        this.request.abort();
    }
}

new HTTPStream('test.php', (m) => console.log(m));

Here is a log:

---

EDIT:

By suggestions, I tried doing this, but unfortunately you can set it to writable only once, and that is it. I have lots of outputs, not just once.