add: forum/components/UserPageSidebar

- extracted from UserPage, replaces affixSidebar util

js/src/forum/components/UserPageSidebar.js

@@ -0,0 +1,42 @@
+import Component from "../../common/Component";
+
+export default class UserPageSidebar extends Component {
+  view(vnode) {
+    return (
+      <nav className="sideNav UserPage-nav">
+        <ul>{vnode.children}</ul>
+      </nav>)
+  }
+
+  onresize(vnode) {
+    const $sidebar = $(vnode.dom);
+    const $header = $('#header');
+    const $footer = $('#footer');
+    const $affixElement = $sidebar.find('> ul');
+
+    $(window).off('.affix');
+    $affixElement.removeClass('affix affix-top affix-bottom').removeData('bs.affix');
+
+    // Don't affix the sidebar if it is taller than the viewport (otherwise
+    // there would be no way to scroll through its content).
+    if ($sidebar.outerHeight(true) > $(window).height() - $header.outerHeight(true)) return;
+
+    $affixElement.affix({
+      offset: {
+        top: () => $sidebar.offset().top - $header.outerHeight(true) - parseInt($sidebar.css('margin-top'), 10),
+        bottom: () => (this.bottom = $footer.outerHeight(true)),
+      },
+    });
+  };
+
+  oncreate(vnode) {
+    super.oncreate(vnode);
+
+    // Register the affix plugin to execute on every window resize (and trigger)
+    $(window).on('resize', this.onresize.bind(this, vnode)).resize();
+  }
+
+  onremove(vnode) {
+    $(window).off('resize', this.onresize.bind(this, vnode));
+  }
+}