Add with-google-analytics example

[prichodko]

Adds an example showing how to setup global site tag - gtag.js to send event data to Google Analytics.

gtag.js replaces older analytics.js solution and is currently recommended by Google - https://developers.google.com/analytics/devguides/collection/gtagjs/migration

Related: #160

[Vadorequest]

@prichodko Beware to apply this:

  GA.set({page: pageName})
  GA.pageview(pageName)

I've read somewhere that doing a simple pageview isn't good, since it put the GA in some kind of broken state because it doesn't know that the page has changed if you don't use set. (and messes up other calls by providing the wrong page)

[prichodko]

@Vadorequest thanks for checking out and yes, this is true for old analytics.js - docs, but is different with the new gtag.js - docs.

[mattiascibien]

@prichodko I think you should format the code using standard for the travis-ci build to pass and the therefore the code-coverage.

[prichodko]

@mattiascibien thanks! Haven't noticed it. :)

PR updated.

[mattiascibien]

@prichodko in any case I have included the code you provided on my site and it worked like a charm (even with static export). I will do something similar for azure appinsights I guess but I am still experimenting.

[prichodko]

@timneutkens rebased :)

[timneutkens]

const { html, head, errorHtml, chunks } = renderPage()
return { html, head, errorHtml, chunks, styles }

lets do it like in the readme

[prichodko]

Makes sense. Done ✅.

[prichodko]

@timneutkens rebased

[timneutkens]

Nice!

[kachkaev]

Thanks for this example @prichodko! It'd be great if GA_TRACKING_ID was coming from process.env – that way it's easier to configure dev vs production.

This is roughly how I approached this a few months back: https://gitlab.com/kachkaev/website-frontend/commit/c36a04d7674ca572f90374bbf83c02d1bde11300

[prichodko]

@kachkaev you are definitely right! I tried to keep example as simple as possible. However for the env variables I would currently use a new feature released in 5.1 - https://zeit.co/blog/next5-1#environment-configuration. What do you think?