Firebase static assets with an efficient cache and CLS policy

When using Firebase to host static assets, you can configure caching headers to implement an efficient cache policy. By setting appropriate cache-control headers, you can control how long browsers and other clients cache your assets, reducing the need for frequent re-downloads.

Here's how you can configure an efficient cache policy for static assets in Firebase Hosting:

1. Install the Firebase command-line interface (CLI) by running the following command if you haven't already:


npm install -g firebase-tools


2. Set up Firebase for your project by running:


firebase login

firebase init


Follow the prompts to select your project and set up Firebase Hosting.

3. After initializing Firebase, a `firebase.json` file will be created in your project's root directory. Open this file.

4. Locate the `"hosting"` section in `firebase.json`. By default, it will contain a `"public"` property specifying the directory to be hosted. Add a `"headers"` section within `"hosting"` if it doesn't already exist.

5. Within the `"headers"` section, add a `"source"` property with the value `"/**"`. This pattern matches all files in your hosting directory.

6. Add a `"headers"` property within the `"source"` object. Here you can define the cache-control headers.

For example, to set a cache policy that caches assets for one year, you can use the following configuration:


"headers": [


"source": "/**",

"headers": [


"key": "Cache-Control",

"value": "public, max-age=31536000"






In the above example, `"public"` indicates that the response can be cached by both the browser and intermediate caches. `max-age=31536000` sets the maximum time the assets can be cached to one year (in seconds).

7. Save the `firebase.json` file.

8. Deploy your Firebase project by running:


firebase deploy


Firebase Hosting will upload your assets and apply the cache policy defined in the `firebase.json` file.

With this configuration, the browser and other clients will cache your static assets for a long period, reducing the number of requests made to the server and improving the performance of your application.

Remember to consider the trade-off between caching and updating assets. If you frequently update your static assets, you may need to reduce the cache duration or implement cache busting techniques when deploying new versions of your assets.

Client code configuration HTML

The `<picture>` element in HTML provides a way to define multiple sources for an image, allowing the browser to select the most appropriate source based on factors such as the user's device, screen size, or other conditions. It is commonly used to implement responsive images or to provide different versions of an image based on different scenarios.

Here's how the `<picture>` element is structured:


<source media="(max-width: 799px)" srcset="Sergej_Dergatsjev_640w.webp" />
<source media="(min-width: 800px)" srcset="Sergej_Dergatsjev_800w.jpg" />
<img src="Sergej_Dergatsjev-640w.jpg" alt="Sergej Dergatsjev" />


Inside the `<picture>` element, you can include one or more `<source>` elements, each with its own `srcset` and `type` attributes. The `srcset` attribute specifies the image source URL and can contain multiple sources separated by commas. Each source can have different resolutions or formats. The `type` attribute indicates the MIME type of the image.

The browser evaluates the `<source>` elements from top to bottom and selects the first source that it can handle based on the `type` attribute and the browser's capabilities. If none of the sources are supported, the browser falls back to the `<img>` element inside the `<picture>` element.

The `<img>` element specifies the fallback image source using the `src` attribute. This source will be used if none of the `<source>` elements are compatible or if the browser does not support the `<picture>` element.

By providing multiple sources in the `<picture>` element, you can optimize the image delivery for different devices or network conditions. For example, you can offer a high-resolution image in one format for devices with high pixel density screens (such as Retina displays), while providing a lower-resolution image in another format for devices with lower screen resolutions.

Additionally, you can use media queries in combination with the `<source>` element to further fine-tune which image source is used based on specific viewport sizes or other conditions. This allows you to tailor the image selection to specific breakpoints or device capabilities.

Overall, the `<picture>` element provides a flexible way to deliver appropriate images based on different factors, helping to optimize the user experience and improve performance on various devices and network conditions.

How to fix Cumulative Layout Shift? 

Cumulative Layout Shift (CLS) is a metric that measures visual stability and is important for providing a smooth user experience. To address CLS issues while using Tailwind CSS, you can apply a few techniques:

1. **Specify explicit dimensions**: Ensure that all images and video elements have explicit dimensions set using Tailwind CSS classes such as `w-*` (width) and `h-*` (height). This prevents unexpected shifts when the content loads.

2. **Responsive image containers**: When using images, wrap them in a container with a predefined aspect ratio using the `aspect-w-*` classes provided by Tailwind CSS. For example:
<div class="aspect-w-16 aspect-h-9">
<img src="path/to/image.jpg" alt="Description of the image" class="object-cover">
This ensures that the image container maintains the correct aspect ratio even before the image loads.

3. **Avoid dynamic content resizing**: If you have dynamic content that might change in size or cause layout shifts, consider using appropriate techniques to prevent unexpected shifts. For example, you can use the `transition` classes provided by Tailwind CSS to animate size changes gradually, reducing the impact of sudden layout shifts.

4. **Minimize CSS changes**: Tailwind CSS provides utility classes for various CSS properties. Minimize unnecessary changes to these properties to prevent layout shifts. Instead of modifying properties directly, try to use existing Tailwind CSS classes whenever possible.

5. **Test and adjust**: Use tools like Google's PageSpeed Insights or Lighthouse to identify specific CLS issues. These tools can provide recommendations on specific elements causing layout shifts. Make necessary adjustments to the affected elements using the techniques mentioned above.

Remember that CLS can be influenced by various factors beyond just CSS, such as the loading order of resources or dynamic content changes. Addressing these issues may require a holistic approach that goes beyond CSS adjustments.

By following these guidelines and optimizing your layout with Tailwind CSS, you can help reduce Cumulative Layout Shift and provide a more visually stable user experience.