jQuery Scroll Depth Fix for Google Tag Manager

jquery.scrolldepth.js

/*!
 * @preserve
 * jquery.scrolldepth.js | v0.7
 * Copyright (c) 2014 Rob Flaherty (@robflaherty)
 * Licensed under the MIT and GPL licenses.
 */

if (window.jQuery) {
	;(function ( $, window, document, undefined ) {
	
	  "use strict";
	
	  var defaults = {
	    minHeight: 0,
	    elements: [],
	    percentage: true,
	    userTiming: true,
	    pixelDepth: true,
	    nonInteraction: true
	  };
	
	  var $window = $(window),
	    cache = [],
	    lastPixelDepth = 0,
	    universalGA,
	    classicGA,
	    standardEventHandler;
	
	  /*
	   * Plugin
	   */
	
	  $.scrollDepth = function(options) {
	
	    var startTime = +new Date;
	
	    options = $.extend({}, defaults, options);
	
	    // Return early if document height is too small
	    if ( $(document).height() < options.minHeight ) {
	      return;
	    }
	
	    /*
	     * Determine which version of GA is being used
	     * "ga", "_gaq", and "dataLayer" are the possible globals
	     */
	
	    if (typeof ga === "function") {
	      universalGA = true;
	    }
	
	    if (typeof _gaq !== "undefined" && typeof _gaq.push === "function") {
	      classicGA = true;
	    }
	
	    if (typeof options.eventHandler === "function") {
	      standardEventHandler = options.eventHandler;
	    } else if (typeof dataLayer !== "undefined" && typeof dataLayer.push === "function") {
	      standardEventHandler = dataLayer.push;
	    }
	
	    if (options.percentage) {
	      // Establish baseline (0% scroll)
	      sendEvent('Percentage', 'Baseline');
	    } else if (options.elements) {
	      sendEvent('Elements', 'Baseline');
	    }
	
	    /*
	     * Functions
	     */
	
	    function sendEvent(action, label, scrollDistance, timing) {
	
	      if (standardEventHandler) {
	
	        standardEventHandler({'event': 'ScrollDistance', 'eventCategory': 'Scroll Depth', 'eventAction': action, 'eventLabel': label, 'eventValue': 1, 'eventNonInteraction': options.nonInteraction});
	
	        if (options.pixelDepth && arguments.length > 2 && scrollDistance > lastPixelDepth) {
	          lastPixelDepth = scrollDistance;
	          standardEventHandler({'event': 'ScrollDistance', 'eventCategory': 'Scroll Depth', 'eventAction': 'Pixel Depth', 'eventLabel': rounded(scrollDistance), 'eventValue': 1, 'eventNonInteraction': options.nonInteraction});
	        }
	
	        if (options.userTiming && arguments.length > 3) {
	          standardEventHandler({'event': 'ScrollTiming', 'eventCategory': 'Scroll Depth', 'eventAction': action, 'eventLabel': label, 'eventTiming': timing});
	        }
	
	      } else {
	
	        if (universalGA) {
	
	          ga('send', 'event', 'Scroll Depth', action, label, 1, {'nonInteraction': options.nonInteraction});
	
	          if (options.pixelDepth && arguments.length > 2 && scrollDistance > lastPixelDepth) {
	            lastPixelDepth = scrollDistance;
	            ga('send', 'event', 'Scroll Depth', 'Pixel Depth', rounded(scrollDistance), 1, {'nonInteraction': options.nonInteraction});
	          }
	
	          if (options.userTiming && arguments.length > 3) {
	            ga('send', 'timing', 'Scroll Depth', action, timing, label);
	          }
	
	        }
	
	        if (classicGA) {
	
	          _gaq.push(['_trackEvent', 'Scroll Depth', action, label, 1, options.nonInteraction]);
	
	          if (options.pixelDepth && arguments.length > 2 && scrollDistance > lastPixelDepth) {
	            lastPixelDepth = scrollDistance;
	            _gaq.push(['_trackEvent', 'Scroll Depth', 'Pixel Depth', rounded(scrollDistance), 1, options.nonInteraction]);
	          }
	
	          if (options.userTiming && arguments.length > 3) {
	            _gaq.push(['_trackTiming', 'Scroll Depth', action, timing, label, 100]);
	          }
	
	        }
	
	      }
	
	    }
	
	    function calculateMarks(docHeight) {
	      return {
	        '25%' : parseInt(docHeight * 0.25, 10),
	        '50%' : parseInt(docHeight * 0.50, 10),
	        '75%' : parseInt(docHeight * 0.75, 10),
	        // 1px cushion to trigger 100% event in iOS
	        '100%': docHeight - 5
	      };
	    }
	
	    function checkMarks(marks, scrollDistance, timing) {
	      // Check each active mark
	      $.each(marks, function(key, val) {
	        if ( $.inArray(key, cache) === -1 && scrollDistance >= val ) {
	          sendEvent('Percentage', key, scrollDistance, timing);
	          cache.push(key);
	        }
	      });
	    }
	
	    function checkElements(elements, scrollDistance, timing) {
	      $.each(elements, function(index, elem) {
	        if ( $.inArray(elem, cache) === -1 && $(elem).length ) {
	          if ( scrollDistance >= $(elem).offset().top ) {
	            sendEvent('Elements', elem, scrollDistance, timing);
	            cache.push(elem);
	          }
	        }
	      });
	    }
	
	    function rounded(scrollDistance) {
	      // Returns String
	      return (Math.floor(scrollDistance/250) * 250).toString();
	    }
	
	    /*
	     * Throttle function borrowed from:
	     * Underscore.js 1.5.2
	     * http://underscorejs.org
	     * (c) 2009-2013 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
	     * Underscore may be freely distributed under the MIT license.
	     */
	
	    function throttle(func, wait) {
	      var context, args, result;
	      var timeout = null;
	      var previous = 0;
	      var later = function() {
	        previous = new Date;
	        timeout = null;
	        result = func.apply(context, args);
	      };
	      return function() {
	        var now = new Date;
	        if (!previous) previous = now;
	        var remaining = wait - (now - previous);
	        context = this;
	        args = arguments;
	        if (remaining <= 0) {
	          clearTimeout(timeout);
	          timeout = null;
	          previous = now;
	          result = func.apply(context, args);
	        } else if (!timeout) {
	          timeout = setTimeout(later, remaining);
	        }
	        return result;
	      };
	    }
	
	    /*
	     * Scroll Event
	     */
	
	    $window.on('scroll.scrollDepth', throttle(function() {
	      /*
	       * We calculate document and window height on each scroll event to
	       * account for dynamic DOM changes.
	       */
	
	      var docHeight = $(document).height(),
	        winHeight = window.innerHeight ? window.innerHeight : $window.height(),
	        scrollDistance = $window.scrollTop() + winHeight,
	
	        // Recalculate percentage marks
	        marks = calculateMarks(docHeight),
	
	        // Timing
	        timing = +new Date - startTime;
	
	      // If all marks already hit, unbind scroll event
	      if (cache.length >= 4 + options.elements.length) {
	        $window.off('scroll.scrollDepth');
	        return;
	      }
	
	      // Check specified DOM elements
	      if (options.elements) {
	        checkElements(options.elements, scrollDistance, timing);
	      }
	
	      // Check standard marks
	      if (options.percentage) {
	        checkMarks(marks, scrollDistance, timing);
	      }
	    }, 500));
	
	  };
	
	})( jQuery, window, document );
}

For this to work in Google Tag Manager,
We have to first ensure that jQuery is available. Sometimes Google Tag Mangager will fire the tag prior to jQuery being available in the window scope.