honor DoNotTrack browser setting wherever possible

_src/_assets/javascripts/bigchain.js

@@ -5,6 +5,7 @@
 //=include bigchain/analytics.js
 //=include bigchain/forms.js
 //=include bigchain/smoothscroll.js
+//=include bigchain/dnt.js
 
 //=include bigchain/form-earlyaccess.js
 
@@ -13,11 +14,14 @@ jQuery(function($) {
     //
     // init modules
     //
-    GoogleAnalytics.init();
     Forms.init();
     SmoothScroll.init();
     FormEarlyAccess.init();
 
+    if (!_dntEnabled()) {
+        GoogleAnalytics.init();
+    }
+
     $('.hero .logo').on('animationend webkitAnimationEnd oAnimationEnd',
         function(e) {
             $('.hero').addClass('is-ready');

_src/_assets/javascripts/bigchain/dnt.js

@@ -0,0 +1,46 @@
+/**
+ * Returns true or false based on whether doNotTack is enabled. It also takes into account the
+ * anomalies, such as !bugzilla 887703, which effect versions of Fx 31 and lower. It also handles
+ * IE versions on Windows 7, 8 and 8.1, where the DNT implementation does not honor the spec.
+ * @see https://bugzilla.mozilla.org/show_bug.cgi?id=1217896 for more details
+ * @params {string} [dnt] - An optional mock doNotTrack string to ease unit testing.
+ * @params {string} [userAgent] - An optional mock userAgent string to ease unit testing.
+ * @returns {boolean} true if enabled else false
+ */
+function _dntEnabled(dnt, userAgent) {
+
+    'use strict';
+
+    // for old version of IE we need to use the msDoNotTrack property of navigator
+    // on newer versions, and newer platforms, this is doNotTrack but, on the window object
+    // Safari also exposes the property on the window object.
+    var dntStatus = dnt || navigator.doNotTrack || window.doNotTrack || navigator.msDoNotTrack;
+    var ua = userAgent || navigator.userAgent;
+
+    // List of Windows versions known to not implement DNT according to the standard.
+    var anomalousWinVersions = ['Windows NT 6.1', 'Windows NT 6.2', 'Windows NT 6.3'];
+
+    var fxMatch = ua.match(/Firefox\/(\d+)/);
+    var ieRegEx = /MSIE|Trident/i;
+    var isIE = ieRegEx.test(ua);
+    // Matches from Windows up to the first occurance of ; un-greedily
+    // http://www.regexr.com/3c2el
+    var platform = ua.match(/Windows.+?(?=;)/g);
+
+    // With old versions of IE, DNT did not exist so we simply return false;
+    if (isIE && typeof Array.prototype.indexOf !== 'function') {
+        return false;
+    } else if (fxMatch && parseInt(fxMatch[1], 10) < 32) {
+        // Can't say for sure if it is 1 or 0, due to Fx bug 887703
+        dntStatus = 'Unspecified';
+    } else if (isIE && platform && anomalousWinVersions.indexOf(platform.toString()) !== -1) {
+        // default is on, which does not honor the specification
+        dntStatus = 'Unspecified';
+    } else {
+        // sets dntStatus to Disabled or Enabled based on the value returned by the browser.
+        // If dntStatus is undefined, it will be set to Unspecified
+        dntStatus = { '0': 'Disabled', '1': 'Enabled' }[dntStatus] || 'Unspecified';
+    }
+
+    return dntStatus === 'Enabled' ? true : false;
+}

_src/_assets/javascripts/bigchain/form-earlyaccess.js

@@ -37,7 +37,9 @@ var FormEarlyAccess = (function(w, d, $) {
                             _config.formBtn.removeClass('disabled');
 
                             // send GA event
-                            GoogleAnalytics.gaEventEarlyAccessSuccess();
+                            if (!_dntEnabled()) {
+                                GoogleAnalytics.gaEventEarlyAccessSuccess();
+                            }
                         },
                         error: function(err) {
                             _config.form.find('.alert-danger').removeClass('hide');
@@ -46,7 +48,9 @@ var FormEarlyAccess = (function(w, d, $) {
                                 .attr('value', 'Send');
 
                             // send GA event
-                            GoogleAnalytics.gaEventEarlyAccessError();
+                            if (!_dntEnabled()) {
+                                GoogleAnalytics.gaEventEarlyAccessError();
+                            }
                         }
                     });
                 }

_src/_includes/scripts.html

@@ -23,6 +23,7 @@ svg4everybody.js
 //
 -->
 <script>
+if (!_dntEnabled()) {
     (function(window) {
 
         // Google Analytics async snippet
@@ -59,6 +60,7 @@ svg4everybody.js
         };
 
     }(window));
+}
 </script>
 
 {% if jekyll.environment == "production" %}