Function intersectionRatio

src/utils/intersection-observer-3p-host.js:120–126

(smaller, larger)

 * @visibleForTesting
 */
export function intersectionRatio(smaller, larger) {
  const smallerBoxArea = smaller.width * smaller.height;
  const largerBoxArea = larger.width * larger.height;

  // Check for a divide by zero
  return largerBoxArea === 0 ? 0 : smallerBoxArea / largerBoxArea;
}

/**
 * Helper function to calculate the IntersectionObserver change entry.