Slight improvement to readability.

src/lazyload-image.ts

@@ -16,12 +16,8 @@ export function isVisible(element: HTMLElement, threshold = 0, _window: Window,
 
     if (scrollContainer) {
         const scrollContainerBounds = Rect.fromElement(scrollContainer);
-        if (scrollContainerBounds.intersectsWith(windowBounds)) {
-            const intersection = scrollContainerBounds.getIntersectionWith(windowBounds);
-            return elementBounds.intersectsWith(intersection);
-        } else {
-            return false;
-        }
+        const intersection = scrollContainerBounds.getIntersectionWith(windowBounds);
+        return elementBounds.intersectsWith(intersection);
     } else {
         return elementBounds.intersectsWith(windowBounds);
     }

src/rect.ts

@@ -1,4 +1,6 @@
 export class Rect {
+    static empty: Rect = new Rect(0, 0, 0, 0);
+
     left: number;
     top: number;
     right: number;
@@ -40,6 +42,10 @@ export class Rect {
         const right = Math.min(this.right, rect.right);
         const bottom = Math.min(this.bottom, rect.bottom);
 
-        return new Rect(left, top, right, bottom);
+        if (right >= left && bottom >= top) {
+            return new Rect(left, top, right, bottom);
+        } else {
+            return Rect.empty;
+        }
     }
 }

test/rect.test.ts

@@ -342,5 +342,20 @@ describe('Rect', () => {
             is(result.bottom, 20);
             is(result.left, 10);
         });
+
+        it('Should return an empty Rect if two Rect\'s don\'t intersect', () => {
+            // Arrange
+            const rectA = new Rect(0, 0, 20, 20);
+            const rectB = new Rect(30, 30, 50, 50);
+
+            // Act
+            const result = rectA.getIntersectionWith(rectB);
+
+            // Assert
+            is(result.top, 0);
+            is(result.right, 0);
+            is(result.bottom, 0);
+            is(result.left, 0);
+        });
     });
 });