Use localStorage for Google Analytics tracking when available

TL;DR:

(function(b,o,i,l,e,r){b.GoogleAnalyticsObject=l;b[l]||(b[l]=
function(){(b[l].q=b[l].q||[]).push(arguments)});b[l].l=+new Date;
e=o.createElement(i);r=o.getElementsByTagName(i)[0];
e.src='//www.google-analytics.com/analytics.js';
r.parentNode.insertBefore(e,r)}(window,document,'script','ga'));
ga('create','UA-XXXXX-X',{'storage': 'none','clientId':localStorage.getItem('gaClientId')});
ga(function(t){localStorage.setItem('gaClientId',t.get('clientId'));});
ga('send','pageview');

---

The Source: http://stackoverflow.com/questions/4502128/convert-google-analytics-cookies-to-local-session-storage/19207035?noredirect=1#19207035

Google Analytics Docs: https://developers.google.com/analytics/devguides/collection/analyticsjs/domains#disableCookies

We could use Modernizer.localstorage to check for localStorage support and fallback to cookies if its not available. Though I’m not sure if we want to lock in Modernizr as a dependency.

Why? Because Google doesn’t need to send their cookie to your server for every single request to your domain (or theirs, for that matter).

[davidmurdoch]

Update:

It is not against TOS to use localStorage to store the ClientID; it is now officially supported by Google: https://developers.google.com/analytics/devguides/collection/analyticsjs/cookies-user-id#using_localstorage_to_store_the_client_id

Note: if you have to support (extremely) old browsers (like iOS5 and FF4) their example snippet may fail (see: https://github.com/Modernizr/Modernizr/blob/master/feature-detects/storage/localstorage.js).

[philipwalton]

Using HTTP State Management mechanisms" (read: localStorage) to propagate cookie state is a circumvention of our privacy safeguards. Doing so violates the Google Analytics Terms of Service

Hmmm, I don’t think this is true. There are opt-out features that GA provides (e.g. Chrome extensions) that don’t rely on the implementor using cookies. I think the point of this section of the TOS is that you can’t create a mechanism by which someone who’s using an official “do not track” extension will still be tracked.

I can look into it further and I’ll update this thread is my assumptions turn out to be false.