From 57924cac791efffdba12c9c0505fc8730d47afc9 Mon Sep 17 00:00:00 2001
From: SleepWalker <mybox@udf.su>
Date: Fri, 3 Jun 2016 23:51:45 +0300
Subject: [PATCH] #131: simple scrollTo animation

---
 src/components/ui/scrollTo.js | 28 ++++++++++++++++++++++++++++
 src/index.js                  |  3 ++-
 2 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 src/components/ui/scrollTo.js

diff --git a/src/components/ui/scrollTo.js b/src/components/ui/scrollTo.js
new file mode 100644
index 0000000..dbcdbf5
--- /dev/null
+++ b/src/components/ui/scrollTo.js
@@ -0,0 +1,28 @@
+/**
+ * Implements scroll to animation with momentum effect
+ */
+
+const requestAnimationFrame = window.requestAnimationFrame || window.mozRequestAnimationFrame
+    || window.webkitRequestAnimationFrame || window.msRequestAnimationFrame;
+
+const DURATION = 500;
+export default function scrollTo(y) {
+    const start = Date.now();
+    const {scrollTop} = document.body;
+    const delta = y - scrollTop;
+
+    requestAnimationFrame(function animateScroll() {
+        const elapsed = Date.now() - start;
+
+        let interpolatedY = scrollTop + delta * (elapsed / DURATION);
+
+        if (interpolatedY < y) {
+            requestAnimationFrame(animateScroll);
+        } else {
+            interpolatedY = y;
+        }
+
+        window.scrollTo(0, interpolatedY);
+    });
+}
+
diff --git a/src/index.js b/src/index.js
index bb6d117..ec4ebce 100644
--- a/src/index.js
+++ b/src/index.js
@@ -53,6 +53,7 @@ userFactory(store)
 
 });
 
+import scrollTo from 'components/ui/scrollTo';
 const SCROLL_ANCHOR_OFFSET = 80; // 50 + 30 (header height + some spacing)
 /**
  * Scrolls to page's top or #anchor link, if any
@@ -73,7 +74,7 @@ function restoreScroll() {
             y = scrollTop + top - SCROLL_ANCHOR_OFFSET;
         }
 
-        window.scrollTo(0, y);
+        scrollTo(y);
     }, 100);
 }