Merge pull request #172 from joinhandshake/skovy/safely-navigate-null-scroll-component

Safely navigate a null scroll component (offsetHeight of null)

Author: danbovey

dist/InfiniteScroll.js

@@ -166,7 +166,7 @@ var InfiniteScroll = (function(_Component) {
     {
       key: 'getParentElement',
       value: function getParentElement(el) {
-        return el.parentNode;
+        return el && el.parentNode;
       },
     },
     {
@@ -241,9 +241,7 @@ var InfiniteScroll = (function(_Component) {
           if (this.props.isReverse) {
             offset = scrollTop;
           } else {
-            offset =
-              this.calculateTopPosition(el) +
-              (el.offsetHeight - scrollTop - window.innerHeight);
+            offset = this.calculateOffset(el, scrollTop);
           }
         } else if (this.props.isReverse) {
           offset = parentNode.scrollTop;
@@ -253,7 +251,11 @@ var InfiniteScroll = (function(_Component) {
         }
 
         // Here we make sure the element is visible as well as checking the offset
-        if (offset < Number(this.props.threshold) && el.offsetParent !== null) {
+        if (
+          offset < Number(this.props.threshold) &&
+          el &&
+          el.offsetParent !== null
+        ) {
           this.detachScrollListener();
           // Call loadMore after detachScrollListener to allow for non-async loadMore functions
           if (typeof this.props.loadMore === 'function') {
@@ -262,6 +264,19 @@ var InfiniteScroll = (function(_Component) {
         }
       },
     },
+    {
+      key: 'calculateOffset',
+      value: function calculateOffset(el, scrollTop) {
+        if (!el) {
+          return 0;
+        }
+
+        return (
+          this.calculateTopPosition(el) +
+          (el.offsetHeight - scrollTop - window.innerHeight)
+        );
+      },
+    },
     {
       key: 'calculateTopPosition',
       value: function calculateTopPosition(el) {

src/InfiniteScroll.js

@@ -87,7 +87,7 @@ export default class InfiniteScroll extends Component {
   }
 
   getParentElement(el) {
-    return el.parentNode;
+    return el && el.parentNode;
   }
 
   filterProps(props) {
@@ -149,9 +149,7 @@ export default class InfiniteScroll extends Component {
       if (this.props.isReverse) {
         offset = scrollTop;
       } else {
-        offset =
-          this.calculateTopPosition(el) +
-          (el.offsetHeight - scrollTop - window.innerHeight);
+        offset = this.calculateOffset(el, scrollTop);
       }
     } else if (this.props.isReverse) {
       offset = parentNode.scrollTop;
@@ -160,7 +158,10 @@ export default class InfiniteScroll extends Component {
     }
 
     // Here we make sure the element is visible as well as checking the offset
-    if (offset < Number(this.props.threshold) && el.offsetParent !== null) {
+    if (
+      offset < Number(this.props.threshold) &&
+      (el && el.offsetParent !== null)
+    ) {
       this.detachScrollListener();
       // Call loadMore after detachScrollListener to allow for non-async loadMore functions
       if (typeof this.props.loadMore === 'function') {
@@ -169,6 +170,17 @@ export default class InfiniteScroll extends Component {
     }
   }
 
+  calculateOffset(el, scrollTop) {
+    if (!el) {
+      return 0;
+    }
+
+    return (
+      this.calculateTopPosition(el) +
+      (el.offsetHeight - scrollTop - window.innerHeight)
+    );
+  }
+
   calculateTopPosition(el) {
     if (!el) {
       return 0;

test/infiniteScroll_test.js

@@ -75,4 +75,28 @@ describe('InfiniteScroll component', () => {
     InfiniteScroll.prototype.attachScrollListener.restore();
     InfiniteScroll.prototype.scrollListener.restore();
   });
+
+  it('should handle when the scrollElement is removed from the DOM', () => {
+    const loadMore = stub();
+
+    const wrapper = mount(
+      <div>
+        <InfiniteScroll pageStart={0} loadMore={loadMore} hasMore={false}>
+          <div className="child-component">Child Text</div>
+        </InfiniteScroll>
+      </div>,
+    );
+
+    const component = wrapper.find(InfiniteScroll);
+
+    // The component has now mounted, but the scrollComponent is null
+    component.instance().scrollComponent = null;
+
+    // Invoke the scroll listener which depends on the scrollComponent to
+    // verify it executes properly, and safely navigates when the
+    // scrollComponent is null.
+    component.instance().scrollListener();
+
+    expect(wrapper.text()).to.contain('Child Text');
+  });
 });