rollup merge of rust-lang#21494: jatinn/jsnav

Added javascript code to insert next/prev links in the rust book.
Related Issue - rust-lang#20835

src/rustbook/css.rs

@@ -48,6 +48,7 @@ body {
     margin-left: auto;
     margin-right:auto;
     max-width: 750px;
+    padding-bottom: 50px;
 }
 
 .chapter {
@@ -125,4 +126,12 @@ body {
     padding: 0;
 }
 
+.left {
+    float: left;
+}
+
+.right {
+    float: right;
+}
+
 "#;

src/rustbook/javascript.rs

@@ -38,6 +38,37 @@ document.addEventListener("DOMContentLoaded", function(event) {
        el.className = classes.join(' ');
      }
   }
+
+  // The below code is used to add prev and next navigation links to the bottom
+  // of each of the sections.
+  // It works by extracting the current page based on the url and iterates over
+  // the menu links until it finds the menu item for the current page. We then
+  // create a copy of the preceeding and following menu links and add the
+  // correct css class and insert them into the bottom of the page.
+  var toc = document.getElementById('toc').getElementsByTagName('a');
+  var href = document.location.pathname.split('/').pop();
+  if (href === 'index.html' || href === '') {
+    href = 'README.html';
+  }
+
+  for (var i = 0; i < toc.length; i++) {
+    if (toc[i].attributes['href'].value === href) {
+      var nav = document.createElement('p');
+      if (i > 0) {
+        var prevNode = toc[i-1].cloneNode(true);
+        prevNode.className = 'left';
+        nav.appendChild(prevNode);
+      }
+      if (i < toc.length - 1) {
+        var nextNode = toc[i+1].cloneNode(true);
+        nextNode.className = 'right';
+        nav.appendChild(nextNode);
+      }
+      document.getElementById('page').appendChild(nav);
+      break;
+    }
+  }
+
 });
 </script>
 "#;