How to access response body as text in https module

I am trying to do the following to parse an html document:

function process_url_handler(res) {
     // ...
     const node = xpath.fromPageSource(res);
}

for (const url of urls) {
    console.log(`${'-'.repeat(10)} ${url} ${'-'.repeat(10)}`);
    let request = https.get(url, (res) => process_url_handler(res));

Res is of type IncomingMessage. How would I get that as raw text so I can grab the html node?