Resize Observer

Summary

An API that notifies you when an element's size changes — more efficient and accurate than listening to the window's `resize` event for element-level responsiveness. Component-level observation is valuable for reusable interfaces because a component's available space can change even when the browser window itself does not.

• 1Use it to adjust a component's layout when its container (not the window) resizes. Verify the behavior with realistic data and handle the failure or empty state as well.
• 2Compare it to `window.addEventListener('resize', ...)` and note the difference in scope. Write down when you would choose each option and what trade-off drives that choice.
• 3Build a chart or card that re-flows its content based on its own measured width.