rename utils.js -> helpers.js

Author: bySabi

src/helpers.js

@@ -0,0 +1,48 @@
+import warning from 'fbjs/lib/warning';
+import { setTimeout } from 'requestanimationframe-timer';
+
+export function animateScroll (id, animate) {
+  const element = id ? document.getElementById(id) : document.body;
+  warning(element, `Cannot find element: #${id}`);
+
+  if (!element) {
+    return null;
+  }
+
+  const { offset, duration, easing } = animate;
+  const start = getScrollTop();
+  const to = getOffsetTop(element) + offset;
+  const change = to - start;
+
+  function animateFn (elapsedTime = 0) {
+    const increment = 20;
+    const elapsed = elapsedTime + increment;
+    const position = easing(null, elapsed, start, change, duration);
+    setScrollTop(position);
+    elapsed < duration &&
+      setTimeout(function () {
+        animateFn(elapsed);
+      }, increment);
+  }
+
+  animateFn();
+  return id;
+}
+
+export function updateHistory (id) {
+  window.location.hash = id;
+}
+
+function getScrollTop () {
+  // like jQuery -> $('html, body').scrollTop
+  return document.documentElement.scrollTop || document.body.scrollTop;
+}
+
+function setScrollTop (position) {
+  document.documentElement.scrollTop = document.body.scrollTop = position;
+}
+
+function getOffsetTop (element) {
+  const { top } = element.getBoundingClientRect();
+  return top + getScrollTop();
+}