Partials empowers developers to optimize web interactions by offloading certain tasks from the user’s device to Deco’s Edge Servers. This innovative approach significantly reduces the amount of JavaScript required to run websites, resulting in faster page load times and improved conversion rates.

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Introduction to Partials

Partials, inspired by htmx, operate by intercepting user interactions on button, anchor, and form elements. These interactions are automatically offloaded to our server, where they generate a new User Interface (UI) state. This fresh UI state is transmitted as pure HTML back to the user’s browser. Our runtime seamlessly replaces and hydrates the new UI state, creating the illusion of client-side interactivity. In reality, the entire computation process occurs in mere milliseconds on our Edge Servers. For more detailed information on Partials, please consult Fresh’s documentation.

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Simplifying Development

While Fresh Partials introduce a new realm of performance optimization, they also bring added complexity to the development cycle. Developers now need to consider multiple rendering modes, their impact on bundle and HTML sizes, interaction latencies, and how to properly navigate partially rendered pages. To streamline this process, Deco has integrated Partials into a higher abstraction layer of our framework, eliminating the need for developers to grapple with these complexities.

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Leveraging Partials for Sections

At Deco, all Sections are treated as partials. This means you can seamlessly incorporate client-side interactivity into any Section without compromising bundle sizes or initial page loads. This is particularly beneficial for creating common UI components such as SKU selectors, infinite scroll features, and tabs. In the following sections, we’ll delve into harnessing the full potential of Partials by creating a lightning-fast SKU selector.

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Example: SKU Selector

SKU selectors enable shoppers to explore different variations of a product, each with its unique set of prices, images, and availability. Consider the example below: sku-selector As demonstrated, altering the selected SKU can result in significant changes to the page. A straightforward approach is to create a signal to store the currently selected SKU and update it on each click: 
// sections/ProductDetails.tsx
export default function ProductDetails ({ skus }) {
  const selectedSku = useSignal(skus[0]);
  
  return (
    <div>
      <ImageSlider sku={selectedSku} />
      <ProductPrice sku={selectedSku}>

      Color:
      <ul>
        <li>
          <button onClick={() => { selectedSku.value = skus[0] }}>Red</button>
        </li>
        <li>
          <button onClick={() => { selectedSku.value = skus[1] }}>Blue</button>
        </li>
        <li>
          <button onClick={() => { selectedSku.value = skus[2] }}>Green</button>
        </li>
      </ul>
    </div>
  )
}
However, this implementation has a downside. To enable interactivity, the entire section, including all SKU data and component code, is shipped to the browser, resulting in decreased site performance.
Note: If you only isolate the buttons as islands, selecting an SKU will not update the displayed price or image, leading to an inconsistent UI.
An alternative approach is to transform the buttons into anchor tags, triggering a new page load upon each SKU selection: 
// sections/ProductDetails.tsx
export default function ProductDetails ({ skus }) {
  return (
    <div>
      <ImageSlider sku={selectedSku} />
      <ProductPrice sku={selectedSku}>

      Color:
      <ul>
        <li>
          <a href={skus[0].url}>Red</a>
        </li>
        <li>
          <a href={skus[1].url}>Blue</a>
        </li>
        <li>
          <a href={skus[2].url}>Green</a>
        </li>
      </ul>
    </div>
  )
}
While this approach offers optimal performance by eliminating the need for islands, it comes at the cost of user experience (UX). With every SKU selection, the page reloads, and the user is taken back to the top of the page. To strike a balance between UX and performance, let’s refactor this component using Partials.

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Enhancing UX and Performance with Partials

// sections/ProductDetails.tsx
import { usePartialSection } from "deco/hooks/usePartialSection.ts";

export default function ProductDetails ({ skus }) {
  return (
    <div>
      <ImageSlider sku={selectedSku} />
      <ProductPrice sku={selectedSku}>

      Color:
      <ul>
        <li>
          <button {...usePartialSection({ href: skus[0].url })}>Red</button>
        </li>
        <li>
          <button {...usePartialSection({ href: skus[1].url })}>Blue</button>
        </li>
        <li>
          <button {...usePartialSection({ href: skus[2].url })}>Green</button>
        </li>
      </ul>
    </div>
  )
}
The magic here lies in the usePartial hook combined with the button tag. This hook accepts an href parameter and enhances the button tag. When the user clicks the button, it triggers client-side navigation and applies HTML diff updates. This approach eliminates the need for islands, boosting performance, while maintaining the scroll position for an improved user experience.

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Example: Tabs

While we’ve explored how to leverage Partials for SKU selectors, tabbed navigation presents a unique challenge. Tabs lack canonical URLs, making it challenging to manage state transitions. However, the usePartialSection hook allows us to override the props that a section uses for rendering, simplifying the process: 
import { usePartialSection } from "deco/hooks/usePartialSection.ts";

interface Props {
  activeIndex: number;
}

const TabbedSection = ({ activeIndex }) => {
  return (
    <div>
      <button
        class={activeIndex === 0 && "active"}
        {...usePartialSection<typeof TabbedSection>({
          props: { activeIndex: 0 },
        })}
      >
        Tab 1
      </button>
      <button
        class={activeIndex === 1 && "active"}
        {...usePartialSection<typeof TabbedSection>({
          props: { activeIndex: 1 },
        })}
      >
        Tab 2
      </button>
      <button
        class={activeIndex === 2 && "active"}
        {...usePartialSection<typeof TabbedSection>({
          props: { activeIndex: 2 },
        })}
      >
        Tab 3
      </button>
    </div>
  );
};
In this example, the activeIndex prop is overridden with each usePartialSection call, simplifying the use of Partials and eliminating the need to manage URLs and search parameters within our sections.