Highlight anchors in the page contents navigation, on scroll

app/assets/javascripts/application.js

@@ -1 +1,7 @@
+// from govuk_frontend_toolkit
+//= require govuk/stick-at-top-when-scrolling
+//= require govuk/stop-scrolling-at-footer
 //= require_tree .
+
+window.GOVUK.stickAtTopWhenScrolling.init();
+window.GOVUK.stopScrollingAtFooter.addEl($('.js-stick-at-top-when-scrolling'));

app/assets/javascripts/modules/highlight-active-section-heading.js

@@ -0,0 +1,150 @@
+;(function (Modules, root) {
+  'use strict'
+
+  var $ = root.$
+  var $window = $(root)
+
+  Modules.HighlightActiveSectionHeading = function () {
+    var self = this
+    var _hasResized = true
+    var _hasScrolled = true
+    var _interval = 50
+    var anchorIDs = []
+
+    self.getWindowDimensions = function () {
+      return {
+        height: $window.height(),
+        width: $window.width()
+      }
+    }
+
+    self.getWindowPositions = function () {
+      return {
+        scrollTop: $window.scrollTop()
+      }
+    }
+
+    self.getElementOffset = function ($el) {
+      return $el.offset()
+    }
+
+    self.start = function ($el) {
+      $window.resize(self.hasResized)
+      $window.scroll(self.hasScrolled)
+
+      setInterval(self.checkResize, _interval)
+      setInterval(self.checkScroll, _interval)
+
+      self.$anchors = $el.find('.js-page-contents a')
+      self.getAnchors()
+
+      self.checkResize()
+      self.checkScroll()
+    }
+
+    self.hasResized = function () {
+      _hasResized = true
+      return _hasResized
+    }
+
+    self.hasScrolled = function () {
+      _hasScrolled = true
+      return _hasScrolled
+    }
+
+    self.checkResize = function () {
+      if (_hasResized) {
+        _hasResized = false
+        _hasScrolled = true
+      }
+    }
+
+    self.checkScroll = function () {
+      if (_hasScrolled) {
+        _hasScrolled = false
+        var windowDimensions = self.getWindowDimensions()
+        if ( windowDimensions.width <= 768) {
+          self.removeActiveItem()
+        } else {
+          self.updateActiveNavItem()
+        }
+      }
+    }
+
+    self.getAnchors = function () {
+      $.each(self.$anchors, function(i) {
+        var anchorID = $(this).attr('href')
+        // e.g. anchorIDs['#meeting-the-digital-service-standard', '#understand-your-users', '#research-continually']
+        anchorIDs.push(anchorID)
+      })
+    }
+
+    self.getHeadingPosition = function ($theID) {
+      return $theID.offset()
+    }
+
+    self.getNextHeadingPosition = function ($theNextID) {
+      return $theNextID.offset()
+    }
+
+    self.getFooterPosition = function ($theID) {
+      return $theID.offset()
+    }
+
+    self.getDistanceBetweenHeadings = function (headingPosition, nextHeadingPosition) {
+      var distanceBetweenHeadings = (nextHeadingPosition - headingPosition)
+      return distanceBetweenHeadings
+    }
+
+    self.updateActiveNavItem = function () {
+      var windowVerticalPosition = self.getWindowPositions().scrollTop
+      var footerPosition = self.getFooterPosition($('#footer'))
+
+      $.each(self.$anchors, function(i) {
+
+        var theID = anchorIDs[i]
+        var theNextID = anchorIDs[i + 1]
+
+        var $theID = $(theID)
+        var $theNextID = $(theNextID)
+
+        var headingPosition = self.getHeadingPosition($theID)
+
+        if (!headingPosition) {
+          return
+        }
+
+        headingPosition = headingPosition.top
+        headingPosition = headingPosition - 53 // fix the offset from top of page
+
+        if (theNextID) {
+          var nextHeadingPosition = self.getNextHeadingPosition($theNextID).top
+        }
+
+        var distanceBetweenHeadings = self.getDistanceBetweenHeadings(headingPosition, nextHeadingPosition)
+        if (distanceBetweenHeadings) {
+          var isPastHeading = (windowVerticalPosition >= headingPosition && windowVerticalPosition < (headingPosition + distanceBetweenHeadings))
+        }
+        // when distanceBetweenHeadings is false (as there isn't a next heading)
+        else {
+          var isPastHeading = (windowVerticalPosition >= headingPosition && windowVerticalPosition < footerPosition.top)
+        }
+
+        if (isPastHeading) {
+          self.setActiveItem(theID)
+        }
+
+      })
+
+    }
+
+    self.setActiveItem = function (theID) {
+      self.$anchors.removeClass('active')
+      self.$anchors.filter("[href='" + theID + "']").addClass('active')
+    }
+
+    self.removeActiveItem = function () {
+      self.$anchors.removeClass('active')
+    }
+  }
+})(window.GOVUK.Modules, window)

app/assets/stylesheets/modules/_govspeak-wrapper.scss

@@ -4,4 +4,21 @@
   @include media(tablet) {
     padding-top: 1.875em;
   }
+
+  .govuk-govspeak p,
+  .govuk-govspeak ol,
+  .govuk-govspeak ul {
+    // govspeak margin bottom is 20px
+    margin-bottom: $gutter-half;
+  }
+
+  .govuk-govspeak h2 {
+    margin-top: 15px;
+    padding-top: 15px;
+    // govspeak margin-top is 45px
+    @include media(tablet) {
+      margin-top: 15px;
+      padding-top: 30px;
+    }
+  }
 }

app/assets/stylesheets/modules/_page-contents.scss

@@ -3,6 +3,7 @@
 
   @include media(tablet) {
     margin-top: 2em;
+    padding-bottom: 4em;
   }
 
   &__title {
@@ -35,4 +36,8 @@
       text-decoration: underline;
     }
   }
+  // Styles required by GOVUK.HighlightActiveNavItem JS
+  &__list .active {
+    font-weight: bold;
+  }
 }

app/views/content_items/service_manual_guide.html.erb

@@ -59,11 +59,11 @@
   </div>
 </div>
 
-<div class="grid-row">
+<div class="grid-row" data-module="highlight-active-section-heading">
   <div class="column-third">
 
     <!--  Page contents -->
-    <div class="page-contents">
+    <div class="page-contents js-page-contents js-stick-at-top-when-scrolling js-sticky-resize">
       <h2 class="page-contents__title">Page contents:</h2>
       <ul class="page-contents__list">
         <% @content_item.header_links.each do |header_link| %>

spec/javascripts/highlight-active-section-heading-spec.js

@@ -0,0 +1,95 @@
+/* eslint-env jasmine */
+/* eslint-disable no-multi-str */
+
+describe('A highlight active section heading module', function () {
+  'use strict'
+
+  var module
+  var $element
+
+  beforeEach(function () {
+    module = new GOVUK.Modules.HighlightActiveSectionHeading()
+
+    $element = $('<div class="grid-row" data-module="highlight-active-section-heading">\
+      <div class="column-third">\
+        <div class="page-contents js-page-contents js-stick-at-top-when-scrolling">\
+          <h2 class="page-contents__title">Page contents:</h2>\
+          <ul class="page-contents__list">\
+            <li><a href="#section-1">Section 1</a></li>\
+            <li><a href="#section-2">Section 2</a></li>\
+            <li><a href="#section-3">Section 3</a></li>\
+          </ul>\
+        </div>\
+      </div>\
+      <div class="column-two-thirds">\
+        <div class="govspeak-wrapper">\
+          <div class="govuk-govspeak">\
+            <h2 id="section-1">Section 1</h2>\
+            <p>Section 1 text</p>\
+            <h2 id="section-2">Section 2</h2>\
+            <p>Section 2 text</p>\
+            <h2 id="section-3">Section 3</h2>\
+            <p>Section 3 text</p>\
+          </div>\
+        </div>\
+      </div>\
+    </div>')
+
+    module.getWindowDimensions = function () {
+      return {
+        height: 768,
+        width: 1024
+      }
+    }
+    module.getFooterPosition = function () {
+      return {
+        top: 500
+      }
+    }
+    module.getHeadingPosition = function () {
+      return {
+        top: 100
+      }
+    }
+    module.getNextHeadingPosition = function () {
+      return {
+        top: 200
+      }
+    }
+  })
+
+  afterEach(function () {
+    $(document).off()
+  })
+
+  // The anchor link with the href matching testHref should be highlighted
+  function isLinkHighlighted (testHref) {
+    var $anchor = $element.find('.js-page-contents a[href="' + testHref + '"]')
+    expect($anchor.hasClass('active')).toBe(true)
+  }
+
+  it('When the page loads, it has no highlighted nav items', function () {
+    module.getWindowPositions = function () {
+      return {
+        scrollTop: 0
+      }
+    }
+    module.start($element)
+
+    var $anchors = $element.find('.js-page-contents a')
+    expect($anchors.hasClass('active')).toBe(false)
+  })
+
+  it('When the page is scrolled, it highlights a nav item', function () {
+    module.getWindowPositions = function () {
+      return {
+        scrollTop: 180
+      }
+    }
+    module.start($element)
+
+    var $anchors = $element.find('.js-page-contents a')
+
+    isLinkHighlighted('#section-3')
+  })
+})