Add initializer which scrolls to #user-content-X

Author: kivikakk

app/initializers/hashchange.js

@@ -0,0 +1,48 @@
+function decodeFragmentValue(hash) {
+    try {
+        return decodeURIComponent(hash.slice(1));
+    } catch (_) {
+        return '';
+    }
+}
+
+function findElementByFragmentName(document, name) {
+    if (name === '') {
+        return;
+    }
+
+    return document.getElementById(name) || document.getElementsByName(name)[0];
+}
+
+function hashchange() {
+    if (document.querySelector(':target')) {
+        return;
+    }
+
+    const hash = decodeFragmentValue(location.hash);
+    const target = findElementByFragmentName(document, `user-content-${hash}`);
+    if (target) {
+        target.scrollIntoView();
+    }
+}
+
+export function initialize(application) {
+    $(window).on('hashchange', hashchange);
+
+    // If clicking on a link to the same fragment as currently in the address bar,
+    // hashchange won't be fired, so we need to manually trigger rescroll.
+    $(document).on('a[href]', 'click', function(event) {
+        if (this.href === location.href && location.hash.length > 1) {
+            setTimeout(function() {
+                if (!event.defaultPrevented) {
+                    hashchange();
+                }
+            });
+        }
+    });
+}
+
+export default {
+    name: 'app.hashchange',
+    initialize
+};