1 files changed, 63 insertions, 0 deletions
diff --git a/polygerrit-ui/app/elements/shared/gr-page-nav/gr-page-nav.js b/polygerrit-ui/app/elements/shared/gr-page-nav/gr-page-nav.js
new file mode 100644
index 0000000000..4c38e3f904
--- /dev/null
+++ b/polygerrit-ui/app/elements/shared/gr-page-nav/gr-page-nav.js
@@ -0,0 +1,63 @@
+// Copyright (C) 2017 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+(function() {
+  'use strict';
+
+  Polymer({
+    is: 'gr-page-nav',
+
+    properties: {
+      _headerHeight: Number,
+    },
+
+    attached() {
+      this.listen(window, 'scroll', '_handleBodyScroll');
+    },
+
+    detached() {
+      this.unlisten(window, 'scroll', '_handleBodyScroll');
+    },
+
+    _handleBodyScroll() {
+      if (this._headerHeight === undefined) {
+        let top = this._getOffsetTop(this);
+        // Don't want to include the element that wraps around the nav, start
+        // with its parent.
+        for (let offsetParent = this._getOffsetParent(this.offsetParent);
+           offsetParent;
+           offsetParent = this._getOffsetParent(offsetParent)) {
+          top += this._getOffsetTop(offsetParent);
+        }
+        this._headerHeight = top;
+      }
+
+      this.$.nav.classList.toggle('pinned',
+          this._getScrollY() >= this._headerHeight);
+    },
+
+    /* Functions used for test purposes */
+    _getOffsetParent(element) {
+      if (!element || !element.offsetParent) { return ''; }
+      return element.offsetParent;
+    },
+
+    _getOffsetTop(element) {
+      return element.offsetTop;
+    },
+
+    _getScrollY() {
+      return window.scrollY;
+    },
+  });
+})();