```js
return _.extend(_.strip_empty_properties({
    '$os': _.info.os(),
    '$browser': _.info.browser(userAgent, navigator.vendor, window.opera),
    '$referrer': document.referrer,
    '$referring_domain': _.info.referringDomain(document.referrer),
    '$device': _.info.device(userAgent)
}), {
    '$screen_height': screen.height,
    '$screen_width': screen.width,
    'mp_lib': 'web'
});
```