add scroll tracking option

book/plugin.js

@@ -1,13 +1,94 @@
 require(["gitbook"], function(gitbook) {
+    var cfg;
+
+    var trackScroll = function() {
+        var scrollCfg = cfg.scroll;
+        var gaSend = (scrollCfg.debug ? function() {
+            console.log(arguments);
+        } : window.ga);
+        jQuery(function($) {
+            var startTime = new Date();
+
+            var bookBody = $('.book-body');
+            var bookBodyInner = $('.book-body .body-inner');
+            var bookBodyPage = $('.book-body .body-inner .page-wrapper');
+            var content = $('.page-inner section').last();
+            var foldPos = 0, contentBottomPos = 0, contentMiddlePos = 0, pageBottomPos = 0;
+
+            var hasPassedFold = false, hasPassedContentMiddle = false, hasPassedContentBottom = false, hasPassedPageBottom = false;
+            var lastScrollPos = -1;
+            var getTimeSinceLoadInSeconds = function() {
+                return Math.round((new Date() - startTime) * 0.001);
+            };
+            var trackScrollImpl = function() {
+                //must track both book body and book body inner because chrome and firefox scroll different ones amongst these two
+                //in firefox the scrollbar is on inner, but in chrome the scrollbar is on outer
+                var scrollPos = foldPos + bookBody.scrollTop() + bookBodyInner.scrollTop();
+                if (scrollPos === lastScrollPos) {
+                    return;
+                }
+                lastScrollPos = scrollPos;
+                if (scrollCfg.debug) {
+                    console.log('scrollPos', scrollPos);
+                }
+                if (!hasPassedPageBottom && scrollPos >= pageBottomPos) {
+                    hasPassedPageBottom = true;
+                    gaSend('send', 'event', 'scroll', 'pastPageBottom', document.location.href, getTimeSinceLoadInSeconds());
+                    //clear intervals - we no longer need them
+                    window.clearInterval(trackScrollImplInterval);
+                    window.clearInterval(trackScrollUpdateSizesInterval);
+                }
+                else if (!hasPassedContentBottom && scrollPos >= contentBottomPos) {
+                    hasPassedContentBottom = true;
+                    gaSend('send', 'event', 'scroll', 'pastContentBottom', document.location.href, getTimeSinceLoadInSeconds());
+                }
+                else if (!hasPassedContentMiddle && scrollPos > contentMiddlePos) {
+                    hasPassedContentMiddle = true;
+                    gaSend('send', 'event', 'scroll', 'pastContentMiddle', document.location.href, getTimeSinceLoadInSeconds());
+                }
+                else if (!hasPassedFold && scrollPos > foldPos) {
+                    hasPassedFold = true;
+                    gaSend('send', 'event', 'scroll', 'pastFold', document.location.href, getTimeSinceLoadInSeconds());
+                }
+            };
+            var trackScrollUpdateSizes = function() {
+                foldPos = $(window).height() - $('.book-header').height(); // bookBodyInner.height();
+                contentBottomPos = content.scrollTop() + content.innerHeight();
+                contentMiddlePos = (foldPos + contentBottomPos) * 0.5;
+                pageBottomPos = content.scrollTop() + bookBodyPage.innerHeight();
+                if (scrollCfg.debug) {
+                    console.log('positions', [foldPos, contentMiddlePos, contentBottomPos, pageBottomPos]);
+                }
+            };
+            trackScrollUpdateSizes();
+            var trackScrollImplInterval = window.setInterval(trackScrollImpl, (scrollCfg.interval || 150));
+            var trackScrollUpdateSizesInterval = window.setInterval(trackScrollUpdateSizes, (scrollCfg.interval * 33 || 5000));
+        });
+    };
+
+    var initTrackScroll = function() {
+        if (cfg && cfg.scroll) {
+            if (typeof window.jQuery === 'function') {
+                trackScroll(cfg.scroll);
+            }
+            else {
+                console.log('Need jQuery to track scrolling');
+            }
+        }
+    };
+
     gitbook.events.bind("start", function(e, config) {
         config.ga = config.ga || {};
+        cfg = config.ga;
+        initTrackScroll();
     });
 
     gitbook.events.bind("page.change", function() {
         ga('send', 'pageview');
+        initTrackScroll();
     });
 
     gitbook.events.bind("exercise.submit", function(e, data) {
 
     });
-});
+});

index.js

@@ -9,13 +9,12 @@ module.exports = {
                 var config = this.options.pluginsConfig.ga || {};
                 if (!config.token) throw "Need to option 'token' for Google Analytics plugin";
 
-                return "<script>(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){"
-                + "(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),"
-                + "m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)"
-                + "})(window,document,'script','//www.google-analytics.com/analytics.js','ga');"
-                + "ga('create', '"+config.token+"', 'auto');"
-                + "ga('send', 'pageview');</script>";
+                return "<script>(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){" +
+                    "(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o)," +
+                    "m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)" +
+                    "})(window,document,'script','//www.google-analytics.com/analytics.js','ga');" +
+                    "ga('create','" + config.token + "','auto');ga('send','pageview');</script>";
             }
         }
     }
-};
+};