Merge pull request #54 from davidr64/prevent-calling-intersection-obs…

…erver-for-empty-observers

Prevent enterAll and leaveAll from calling callbacks on observers with no observed nodes

src/mocks/intersection-observer.ts

@@ -168,6 +168,8 @@ export class MockedIntersectionObserver implements IntersectionObserver {
   }
 
   triggerNodes(nodeDescriptions: NodeIntersectionDescription[]) {
+    if (nodeDescriptions.length === 0) return;
+
     const nodeIndexes = nodeDescriptions.map(({ node }) =>
       findNodeIndex(this.nodes, node)
     );