Add support for offset values in isInViewport

app/assets/javascripts/lib/utils/common_utils.js

@@ -118,12 +118,13 @@ export const handleLocationHash = () => {
 
 // Check if element scrolled into viewport from above or below
 // Courtesy http://stackoverflow.com/a/7557433/414749
-export const isInViewport = el => {
+export const isInViewport = (el, offset = {}) => {
   const rect = el.getBoundingClientRect();
+  const { top, left } = offset;
 
   return (
-    rect.top >= 0 &&
-    rect.left >= 0 &&
+    rect.top >= (top || 0) &&
+    rect.left >= (left || 0) &&
     rect.bottom <= window.innerHeight &&
     rect.right <= window.innerWidth
   );

spec/javascripts/lib/utils/common_utils_spec.js

@@ -716,4 +716,29 @@ describe('common_utils', () => {
       expect(commonUtils.roundOffFloat(34567.14159, -5)).toBe(0);
     });
   });
+
+  describe('isInViewport', () => {
+    let el;
+
+    beforeEach(() => {
+      el = document.createElement('div');
+    });
+
+    afterEach(() => {
+      document.body.removeChild(el);
+    });
+
+    it('returns true when provided `el` is in viewport', () => {
+      document.body.appendChild(el);
+
+      expect(commonUtils.isInViewport(el)).toBe(true);
+    });
+
+    it('returns false when provided `el` is not in viewport', () => {
+      el.setAttribute('style', 'position: absolute; top: -1000px; left: -1000px;');
+      document.body.appendChild(el);
+
+      expect(commonUtils.isInViewport(el)).toBe(false);
+    });
+  });
 });