Why Svelte Outperforms React: A Deep Dive into Render Performance

Svelte and React are both popular JavaScript frameworks for building user interfaces. However, Svelte has gained significant attention for its exceptional rendering performance when compared to React. In this blog post, we will take a detailed look at how Svelte’s unique design choices allow it to render and perform better than React.

Compile-time vs. Run-time

The primary difference between Svelte and React lies in their approach to rendering components. React uses a virtual DOM and handles rendering at runtime, while Svelte compiles components down to efficient JavaScript code during build time. This fundamental difference has a significant impact on performance.

Svelte’s compile-time optimisation eliminates the need for a virtual DOM, which leads to smaller bundle sizes and faster rendering. Since Svelte components are precompiled, they require fewer calculations at runtime, resulting in a more efficient and faster rendering process. React, on the other hand, has to perform reconciliation on the virtual DOM at runtime, which can be a more expensive operation.

No Virtual DOM

The virtual DOM is a core feature of React that allows it to efficiently update only the parts of the DOM that have changed. While this approach offers a level of abstraction and improved performance over traditional DOM manipulation, it still comes with a cost.

In Svelte, there is no virtual DOM. Instead, Svelte-generated code directly manipulates the actual DOM, which can be faster than using a virtual DOM. This direct approach eliminates the need for reconciliation and reduces the amount of work required to update the DOM, leading to better performance overall.

Reactive Programming

Svelte leverages reactive programming principles, making it easier to manage component state and automatically updating the DOM when the state changes. In Svelte, the compiler detects state changes and generates the necessary code to update the DOM efficiently. This approach avoids unnecessary updates and ensures that only the parts of the DOM that have changed are updated.

React, on the other hand, uses a more traditional approach to state management, requiring developers to call the setState method and trigger component updates manually. While this gives developers more control, it can also lead to less optimised rendering if not managed carefully.

Bundle Size

Another factor that contributes to Svelte’s superior performance is its smaller bundle size. Since Svelte compiles components into highly optimised JavaScript code during build time, the output is typically smaller than React’s equivalent. A smaller bundle size means faster load times and improved performance, especially on slow or unreliable networks.

Fine-grained Control

Svelte components provide fine-grained control over their lifecycle and updates. Developers can use Svelte’s onMount, beforeUpdate, afterUpdate, and onDestroy methods to manage component updates and optimise performance. This level of control allows developers to write highly optimised components that only update when necessary, resulting in faster rendering times.

Conclusion

Svelte’s compile-time approach, lack of a virtual DOM, reactive programming model, smaller bundle size, and fine-grained control over component updates enable it to render and perform better than React. While React remains a powerful and widely used framework, Svelte’s design choices make it an attractive alternative for developers who prioritise performance and efficiency.