Adapting to Change: How ResizeObserver Can Revolutionize Your UI

The Power of ResizeObserver

As web development continues to evolve, creating user interfaces that adapt to varying screen widths and container widths has become a significant challenge. With the rise of component-based frameworks like React and Vue.js, as well as native web components, building UIs that can adjust to different devices and screen sizes is crucial.

Enter ResizeObserver, a game-changing API that allows you to call a function whenever an element is resized, similar to listening to a window resize event. This powerful tool enables you to create UIs that seamlessly adapt to the user’s screen and container width.

Practical Examples of ResizeObserver in Action

Filling a Container

Imagine you want to display a row of inspirational photos below the hero section of your page. You only want to load as many photos as needed to fill the row, and you want to add or remove photos as necessary whenever the container width changes. ResizeObserver makes this possible.

Here’s an example code snippet:

const ro = new ResizeObserver(entries => {
  for (const entry of entries) {
    const { width } = entry.contentRect;
    // Calculate the number of photos to display based on the container width
    const numPhotos = Math.floor(width / 300);
    // Update the UI accordingly
  }
});

ro.observe(document.getElementById('photo-container'));

See the Pen ResizeObserver – Fill Container by Kevin Drum (@kevinleedrum) on CodePen.

Changing a Flex Row to a Column

Another common problem is converting a flex row of elements into a column when they won’t fit in a single row. With ResizeObserver, this is achievable.

Here’s an example code snippet:

const ro = new ResizeObserver(entries => {
  for (const entry of entries) {
    const { width } = entry.contentRect;
    const elements = document.querySelectorAll('.flex-elements');
    if (width < elements.length * 100) {
      // Switch to column layout
      elements.forEach(element => element.style.flexDirection = 'column');
    } else {
      // Switch to row layout
      elements.forEach(element => element.style.flexDirection = 'row');
    }
  }
});

ro.observe(document.getElementById('flex-container'));

See the Pen ResizeObserver – Flex Direction by Kevin Drum (@kevinleedrum) on CodePen.

Responsive Toolbar Component

Remember the work problem mentioned earlier, where buttons needed to be moved into a dropdown menu responsively? Our final example builds upon the previous one, checking for overflow and repeating the check every time a button is removed.

Here’s an example code snippet:

const ro = new ResizeObserver(entries => {
  for (const entry of entries) {
    const { width } = entry.contentRect;
    const toolbar = document.getElementById('toolbar');
    const buttons = toolbar.querySelectorAll('button');
    if (width < buttons.length * 100) {
      // Move buttons to dropdown menu
    } else {
      // Display buttons in toolbar
    }
  }
});

ro.observe(document.getElementById('toolbar-container'));

See the Pen ResizeObserver – Responsive Toolbar by Kevin Drum (@kevinleedrum) on CodePen.

The Future of Responsive Design

ResizeObserver, alongside CSS media queries and container queries, helps build the foundation of responsive interfaces on the modern web. By leveraging this powerful API, you can create UIs that adapt seamlessly to changing screen widths and container widths, providing a better user experience for your audience.

• Media queries allow you to apply different styles based on specific conditions, such as screen width or device type.
• Container queries enable you to style elements based on the size of their parent container.
• ResizeObserver provides a way to react to changes in element sizes, enabling you to create dynamic and responsive interfaces.

Together, these tools empower you to create responsive designs that adapt to the ever-changing landscape of modern web development.