Programmatically capturing AJAX traffic with headless Chrome

I finally found how to do what I wanted. It can be done with chrome-remote-interface (CRI), and node.js. I'm attaching the minimal code required.

const CDP = require('chrome-remote-interface');

(async function () {

    // you need to have a Chrome open with remote debugging enabled
    // ie. chrome --remote-debugging-port=9222
    const protocol = await CDP({port: 9222});

    const {Page, Network} = protocol;
    await Page.enable();
    await Network.enable(); // need this to call Network.getResponseBody below

    Page.navigate({url: 'http://localhost/'}); // your URL

    const onDataReceived = async (e) => {
        try {
            let response = await Network.getResponseBody({requestId: e.requestId})
            if (typeof response.body === 'string') {
                console.log(response.body);
            }
        } catch (ex) {
            console.log(ex.message)
        }
    }

    protocol.on('Network.dataReceived', onDataReceived)
})();

Update

As @Alejandro pointed out in the comment, resourceType is a function and the return value is lowercased

page.on('request', request => {
    if (request.resourceType() === 'xhr')
    // do something
});

Original answer

Puppeteer's API makes this really easy:

page.on('request', request => {
  if (request.resourceType === 'XHR')
    // do something
});

You can also intercept requests with setRequestInterception, but it's not needed in this example if you're not going to modify the requests.

There's an example of intercepting image requests that you can adapt.

resourceTypes are defined here.

Puppeteer's listeners could help you capture xhr response via response and request event.

You should check wether request.resourceType() is xhr or fetch first.

        listener = page.on('response', response => {
            const isXhr = ['xhr','fetch'].includes(response.request().resourceType())
            if (isXhr){
                console.log(response.url());
                response.text().then(console.log)
            }
        })