next.js/examples/with-higher-order-component/hocs/withUserAgent.js

import { getDisplayName } from '../lib/getDisplayName'

export const withUserAgent = Page => {
  const WithUserAgent = props => <Page {...props} />

  WithUserAgent.getInitialProps = async context => {
    const userAgent = context.req
      ? context.req.headers['user-agent']
      : navigator.userAgent

    return {
      ...(Page.getInitialProps ? await Page.getInitialProps(context) : {}),
      userAgent
    }
  }

  WithUserAgent.displayName = `WithUserAgent(${getDisplayName(Page)})`

  return WithUserAgent
}