Fixes jump to footnote labels on small screens.

Resolves sighingnow#130.

Signed-off-by: Tao He <sighingnow@gmail.com>

Author: sighingnow

_includes/footer.html

@@ -17,6 +17,9 @@
 <script src="../gitbook/gitbook-plugin-search/search.js"></script>
 -->
 
+<script src="{{site.baseurl}}/assets/gitbook/custom.js"></script>
+<script src="{{site.baseurl}}/assets/gitbook/custom-local.js"></script>
+
 {% if site.extra_footer_js %}
     {%- for extra_js in site.extra_header_js -%}
         {%- assign starts_with = extra_js | slice: 0,4  -%}

_includes/toc-date.html

@@ -12,7 +12,12 @@
             $(element).closest('li.chapter').find('ul>li').removeClass('active');
             $(element).parent().addClass('active');
             if ($(document).width() <= 1240) {
-                $('div.body-inner').animate({scrollTop: $($(element).attr('href')).get(0).offsetTop});
+                let target = $($(element).attr('href'));
+                if (target.length) {
+                    $('div.body-inner').animate({
+                        scrollTop: target.get(0).offsetTop,
+                    });
+                }
             }
             return true;
         }

assets/gitbook/custom-local.js

@@ -0,0 +1,29 @@
+// Enable footnote link support for pages with width < 1240.
+//
+function bind_footnote_links() {
+    if ($(document).width() > 1240) {
+        return;
+    }
+    let footnotes = $("div.footnotes").find("ol > li > p > a.reversefootnote");
+    for (let i = 0; i < footnotes.length; i++) {
+        let footnote = footnotes[i];
+        footnote.addEventListener('click', function(e) {
+            e.preventDefault();
+            var target = $($(this).attr('href'));
+            if (target.length) {
+                $('div.body-inner').animate({
+                    scrollTop: target.get(0).offsetTop,
+                });
+            }
+        });
+    }
+}
+
+if (document.readyState === "loading") {
+    // Loading hasn't finished yet
+    document.addEventListener("DOMContentLoaded", bind_footnote_links);
+} else {
+    // `DOMContentLoaded` has already fired
+    bind_footnote_links();
+}
+