1. Data Binding: D3.js relies heavily on data binding, where data values are connected to elements in the DOM to dynamically update the visualization based on changes in the data. Svelte, on the other hand, uses a reactive declaration syntax for data binding, which simplifies the process by automatically updating the DOM when the data changes.
2. Component Architecture: D3.js is a library for manipulating documents based on data and primarily focuses on SVG elements for creating visualizations. In contrast, Svelte is a full-fledged framework that supports building components with reusable code and encapsulated styles, making it easier to manage complex applications.
3. Performance: D3.js renders visualizations directly to the DOM, which can sometimes lead to performance issues when dealing with large datasets or complex animations. Svelte, on the other hand, compiles components into highly optimized vanilla JavaScript code during build time, resulting in faster rendering and improved performance.
4. Learning Curve: D3.js has a steep learning curve due to its low-level API and complex concepts like enter-update-exit pattern for data binding. Svelte, on the other hand, offers a more intuitive and beginner-friendly syntax with reactive declarations and built-in state management, making it easier for developers to create interactive web applications.
5. Bundle Size: D3.js is a comprehensive library with a large file size, requiring developers to selectively import only the modules they need to reduce bundle size. In contrast, Svelte's compiler analyzes and optimizes the code during build time, resulting in smaller bundle sizes and faster load times for web applications.
6. Community Support: D3.js has a strong and active community with a wealth of resources, tutorials, and examples available online. Svelte, being a relatively newer framework, is gradually gaining popularity and community support, but may have fewer resources compared to D3.js.

In Summary, D3.js is more focused on data visualization and manipulation through the DOM, while Svelte provides a framework for building reactive and performant web applications with a simpler syntax and optimized bundle size.