diff --git a/src/animation/rendering.js b/src/animation/rendering.js
index 13631e2..b12f98a 100644
--- a/src/animation/rendering.js
+++ b/src/animation/rendering.js
@@ -1,7 +1,7 @@
 goog.module('clulib.animation.rendering');
 
-const EventTarget = goog.require('goog.events.EventTarget');
 const Event = goog.require('goog.events.Event');
+const EventTarget = goog.require('goog.events.EventTarget');
 
 /**
  * A render loop which runs on requestAnimationFrame.
diff --git a/src/cm/cm.js b/src/cm/cm.js
index 77635df..4ebcd25 100644
--- a/src/cm/cm.js
+++ b/src/cm/cm.js
@@ -1,13 +1,13 @@
 goog.module('clulib.cm');
 
-const {removeHoles, asyncForEachRight} = goog.require('clulib.array');
-const Completer = goog.require('clulib.async.Completer');
-const {closest, matches} = goog.require('clulib.dom');
-
 const {removeDuplicates} = goog.require('goog.array');
-const GoogComponent = goog.require('goog.ui.Component');
 const {assert} = goog.require('goog.asserts');
 const {getParentElement, isElement} = goog.require('goog.dom');
+const GoogComponent = goog.require('goog.ui.Component');
+
+const {removeHoles, asyncForEachRight} = goog.require('clulib.array');
+const Completer = goog.require('clulib.async.Completer');
+const {closest, matches} = goog.require('clulib.dom');
 
 /**
  * Component metadata.
@@ -793,7 +793,7 @@ class NodeTree {
       while (getParentElement(element) !== rootElement) {
         const parent = getParentElement(element);
         if (parent.hasAttribute(this.manager_.getTypeAttribute()) &&
-            parent.hasAttribute(this.manager_.getIdAttribute()))
+          parent.hasAttribute(this.manager_.getIdAttribute()))
           highestComponentElement = parent;
         element = parent;
       }
diff --git a/src/dom/dom.js b/src/dom/dom.js
index f1bef99..6a35a8b 100644
--- a/src/dom/dom.js
+++ b/src/dom/dom.js
@@ -3,6 +3,8 @@ goog.module('clulib.dom');
 const {getAncestor, isElement, getViewportSize} = goog.require('goog.dom');
 const Rect = goog.require('goog.math.Rect');
 
+const {rectangleIntersects} = goog.require('clulib.math');
+
 /**
  * Returns true if the element would be selected by the specified
  * selector string, false otherwise.
@@ -72,25 +74,7 @@ function isElementVisible (element, factor = null) {
    */
   const elementRect = new Rect(boundingRect.left, boundingRect.top, boundingRect.width, boundingRect.height);
 
-  /**
-   * @type {goog.math.Rect}
-   */
-  const intersectionRect = Rect.intersection(viewportRect, elementRect);
-
-  // If no intersection exists or the area is zero, return false
-  if (intersectionRect == null || intersectionRect.getSize().area() === 0)
-    return false;
-
-  // If no percentage calculation is needed, return true
-  if (factor == null)
-    return true;
-
-  const elementArea = elementRect.getSize().area();
-  const intersectionArea = intersectionRect.getSize().area();
-
-  const visibleFactor = intersectionArea / elementArea;
-
-  return visibleFactor >= factor;
+  return rectangleIntersects(viewportRect, elementRect, factor);
 }
 
 exports = {matches, closest, isElementVisible};
diff --git a/src/l10n/resource_bundle.js b/src/l10n/resource_bundle.js
index 206ccb7..4947e1a 100644
--- a/src/l10n/resource_bundle.js
+++ b/src/l10n/resource_bundle.js
@@ -1,8 +1,8 @@
 goog.module('clulib.l10n.ResourceBundle');
 
-const {httpGetJson} = goog.require('clulib.net.http_request');
 const {objectToMap} = goog.require('clulib.collections');
 const {cacheAsyncValue} = goog.require('clulib.functions');
+const {httpGetJson} = goog.require('clulib.net.http_request');
 
 /**
  * A resource bundle containing localized messages.
diff --git a/src/math/math.js b/src/math/math.js
index eacbba0..0afbd10 100644
--- a/src/math/math.js
+++ b/src/math/math.js
@@ -1,5 +1,7 @@
 goog.module('clulib.math');
 
+const Rect = goog.require('goog.math.Rect');
+
 /**
  * Maps a value from one range to another range.
  *
@@ -14,4 +16,33 @@ function mapRange (x, inMin, inMax, outMin, outMax) {
   return (x - inMin) * (outMax - outMin) / (inMax - inMin) + outMin;
 }
 
-exports = {mapRange};
+/**
+ * Returns true if a rectangle intersects another rectangle.
+ *
+ * Takes a factor to specify how much of rectangleB needs to intersect rectangleA.
+ *
+ * @param {goog.math.Rect} rectangleA
+ * @param {goog.math.Rect} rectangleB
+ * @param {?number|null} factor The factor from 0 (not intersecting) to 1 (completely intersecting)
+ * @returns {boolean}
+ */
+function rectangleIntersects (rectangleA, rectangleB, factor = null) {
+  /**
+   * @type {goog.math.Rect}
+   */
+  const intersectionRect = Rect.intersection(rectangleA, rectangleB);
+
+  // If no intersection exists or the area is zero, return false
+  if (intersectionRect == null || intersectionRect.getSize().area() === 0)
+    return false;
+
+  // If no percentage calculation is needed, return true
+  if (factor == null)
+    return true;
+
+  const visibleFactor = intersectionRect.getSize().area() / rectangleB.getSize().area();
+
+  return visibleFactor >= factor;
+}
+
+exports = {mapRange, rectangleIntersects};
diff --git a/src/net/http_request.js b/src/net/http_request.js
index 8a42587..ca5d46d 100644
--- a/src/net/http_request.js
+++ b/src/net/http_request.js
@@ -1,11 +1,12 @@
 goog.module('clulib.net.http_request');
 
-const Completer = goog.require('clulib.async.Completer');
 const events = goog.require('goog.events');
-const XhrIo = goog.require('goog.net.XhrIo');
 const EventType = goog.require('goog.net.EventType');
+const XhrIo = goog.require('goog.net.XhrIo');
 const ResponseType = goog.require('goog.net.XhrIo.ResponseType');
 
+const Completer = goog.require('clulib.async.Completer');
+
 /**
  * @typedef {{
  *   response: *,
diff --git a/src/ui/toggle_button.js b/src/ui/toggle_button.js
index 8eda081..fca8975 100644
--- a/src/ui/toggle_button.js
+++ b/src/ui/toggle_button.js
@@ -1,10 +1,10 @@
 goog.module('clulib.ui.ToggleButton');
 
-const {Component} = goog.require('clulib.cm');
-
-const {contains, enable} = goog.require('goog.dom.classlist');
 const GoogEvent = goog.require('goog.events.Event');
 const GoogEventType = goog.require('goog.events.EventType');
+const {contains, enable} = goog.require('goog.dom.classlist');
+
+const {Component} = goog.require('clulib.cm');
 
 /**
  * @enum {string}
diff --git a/test/animation/rendering_spec.js b/test/animation/rendering_spec.js
index 34a3e4c..1ab945a 100644
--- a/test/animation/rendering_spec.js
+++ b/test/animation/rendering_spec.js
@@ -1,9 +1,10 @@
 goog.module('test.clulib.animation.rendering');
 
+const {listen} = goog.require('goog.events');
+
 const {RenderLoop, RenderLoopEventType} = goog.require('clulib.animation.rendering');
-const {waitFor} = goog.require('testing.async');
 
-const {listen} = goog.require('goog.events');
+const {waitFor} = goog.require('testing.async');
 
 exports = function () {
   describe('clulib.animation.rendering', () => {
diff --git a/test/array/array_spec.js b/test/array/array_spec.js
index f5737d1..847484e 100644
--- a/test/array/array_spec.js
+++ b/test/array/array_spec.js
@@ -1,8 +1,9 @@
 goog.module('test.clulib.array');
 
-const {removeHoles, asyncForEach, asyncForEachRight} = goog.require('clulib.array');
 const {clone} = goog.require('goog.array');
 
+const {removeHoles, asyncForEach, asyncForEachRight} = goog.require('clulib.array');
+
 exports = function () {
   describe('clulib.array', () => {
     describe('removeHoles', () => {
diff --git a/test/async/completer_spec.js b/test/async/completer_spec.js
index 17cfded..c959f13 100644
--- a/test/async/completer_spec.js
+++ b/test/async/completer_spec.js
@@ -1,8 +1,9 @@
 goog.module('test.clulib.async.Completer');
 
-const Completer = goog.require('clulib.async.Completer');
 const AssertionError = goog.require('goog.asserts.AssertionError');
 
+const Completer = goog.require('clulib.async.Completer');
+
 exports = function () {
   describe('clulib.async.Completer', () => {
     it('should resolve its promise', async () => {
diff --git a/test/cm/cm_spec.js b/test/cm/cm_spec.js
index 456d7fb..806f96e 100644
--- a/test/cm/cm_spec.js
+++ b/test/cm/cm_spec.js
@@ -1,10 +1,10 @@
 goog.module('test.clulib.cm');
 
-const {ComponentManager, Component} = goog.require('clulib.cm');
-
-const {appendChild, removeNode, getFirstElementChild} = goog.require('goog.dom');
 const {contains} = goog.require('goog.dom.classlist');
 const {has} = goog.require('goog.dom.dataset');
+const {appendChild, removeNode, getFirstElementChild} = goog.require('goog.dom');
+
+const {ComponentManager, Component} = goog.require('clulib.cm');
 
 exports = function () {
   describe('clulib.cm.ComponentManager', () => {
diff --git a/test/dom/dom_spec.js b/test/dom/dom_spec.js
index 80eccc4..f4bf1ce 100644
--- a/test/dom/dom_spec.js
+++ b/test/dom/dom_spec.js
@@ -1,9 +1,9 @@
 goog.module('test.clulib.dom');
 
-const {matches, closest, isElementVisible} = goog.require('clulib.dom');
-
 const {appendChild, removeNode, getViewportSize} = goog.require('goog.dom');
 
+const {matches, closest, isElementVisible} = goog.require('clulib.dom');
+
 exports = function () {
   describe('clulib.dom', () => {
     describe('matches', () => {
diff --git a/test/l10n/resource_bundle_spec.js b/test/l10n/resource_bundle_spec.js
index be4d727..c703dd2 100644
--- a/test/l10n/resource_bundle_spec.js
+++ b/test/l10n/resource_bundle_spec.js
@@ -1,6 +1,7 @@
 goog.module('test.clulib.l10n.ResourceBundle');
 
 const ResourceBundle = goog.require('clulib.l10n.ResourceBundle');
+
 const env = goog.require('testing.environment');
 
 const base = `${env.basePath}/test-assets/l10n`;
diff --git a/test/l10n/resource_manager_spec.js b/test/l10n/resource_manager_spec.js
index 3e1aabb..b97dfb1 100644
--- a/test/l10n/resource_manager_spec.js
+++ b/test/l10n/resource_manager_spec.js
@@ -1,6 +1,7 @@
 goog.module('test.clulib.l10n.ResourceManager');
 
 const ResourceManager = goog.require('clulib.l10n.ResourceManager');
+
 const env = goog.require('testing.environment');
 
 const base = `${env.basePath}/test-assets/l10n`;
diff --git a/test/math/math_spec.js b/test/math/math_spec.js
index 796f9da..3e6d5d1 100644
--- a/test/math/math_spec.js
+++ b/test/math/math_spec.js
@@ -1,6 +1,9 @@
 goog.module('test.clulib.math');
 
-const {mapRange} = goog.require('clulib.math');
+const Rect = goog.require('goog.math.Rect');
+const Size = goog.require('goog.math.Size');
+
+const {mapRange, rectangleIntersects} = goog.require('clulib.math');
 
 exports = function () {
   describe('clulib.math', () => {
@@ -18,5 +21,68 @@ exports = function () {
         expect(mapRange(-5, -10, 0, -100, 0)).toBe(-50);
       });
     });
+
+    describe('rectangleIntersects', () => {
+      /**
+       * @type {goog.math.Size}
+       */
+      const size = new Size(1024, 768);
+
+      /**
+       * @type {goog.math.Rect}
+       */
+      const rectA = new Rect(0, 0, size.width, size.height);
+
+      it('should detect fully intersecting rectangles', () => {
+        /**
+         * @type {goog.math.Rect}
+         */
+        const fullyVisible = new Rect(
+          size.width / 4,
+          size.height / 4,
+          size.width / 2,
+          size.height / 2
+        );
+
+        expect(rectangleIntersects(rectA, fullyVisible)).toBe(true);
+        expect(rectangleIntersects(rectA, fullyVisible, 1)).toBe(true);
+      });
+
+      it('should detect partially intersecting rectangles', () => {
+        const quarterVisible = new Rect(
+          size.width / 2,
+          size.height / 2,
+          size.width,
+          size.height
+        );
+
+        expect(rectangleIntersects(rectA, quarterVisible)).toBe(true);
+        expect(rectangleIntersects(rectA, quarterVisible, .23)).toBe(true);
+        expect(rectangleIntersects(rectA, quarterVisible, .25)).toBe(true);
+        expect(rectangleIntersects(rectA, quarterVisible, .26)).toBe(false);
+      });
+
+      it('should not detect non intersecting rectangles', () => {
+        const notVisible = new Rect(
+          0,
+          size.height * 2,
+          size.width,
+          size.height
+        );
+
+        expect(rectangleIntersects(rectA, notVisible)).toBe(false);
+      });
+
+      it('should not detect non intersecting rectangles on edge', () => {
+        const notVisibleOnEdge = new Rect(
+          0,
+          size.height,
+          size.width,
+          size.height
+        );
+
+        expect(rectangleIntersects(rectA, notVisibleOnEdge)).toBe(false);
+      });
+    });
   });
 };
diff --git a/test/net/http_request_spec.js b/test/net/http_request_spec.js
index 2d6c927..cd039e5 100644
--- a/test/net/http_request_spec.js
+++ b/test/net/http_request_spec.js
@@ -1,9 +1,11 @@
 goog.module('test.clulib.net.http_request');
 
-const env = goog.require('testing.environment');
-const http = goog.require('clulib.net.http_request');
 const ErrorType = goog.require('goog.net.EventType');
 
+const http = goog.require('clulib.net.http_request');
+
+const env = goog.require('testing.environment');
+
 const jsonFile = `${env.basePath}/test-assets/json/dummy.json`;
 const jsonString = 'Hello, world!';
 
diff --git a/test/validation/validation_spec.js b/test/validation/validation_spec.js
index 9a6c94b..3858451 100644
--- a/test/validation/validation_spec.js
+++ b/test/validation/validation_spec.js
@@ -2,9 +2,10 @@ goog.module('test.clulib.validation');
 
 const ResponseType = goog.require('goog.net.XhrIo.ResponseType');
 
+const http = goog.require('clulib.net.http_request');
 const validation = goog.require('clulib.validation');
+
 const {basePath} = goog.require('testing.environment');
-const http = goog.require('clulib.net.http_request');
 
 /**
  * @returns {Promise<Blob>}