What is the difference between how Solid and Svelte works?

Solid and Svelte are both modern frontend frameworks with significant differences in their design philosophies and implementation. I will explain how they work separately and provide examples.

How Solid Works

Solid is a declarative JavaScript library for building user interfaces, with its core feature being fine-grained reactive programming. Solid operates using a simple observer pattern, where each state variable is an independent reactive signal. When these signals update, only components that depend on them re-render.

For example, if you have a counter component, you might have a state count. In Solid, count will be a signal, and when you update count, only components that depend on count will update. This granular control enables Solid to efficiently update the DOM.

javascript
import { createSignal } from 'solid-js';

function Counter() {
  const [count, setCount] = createSignal(0);

  return (
    <div>
      <p>{count()}</p>
      <button onClick={() => setCount(count() + 1)}>Increment</button>
    </div>
  );
}

How Svelte Works

Svelte differs from Solid in that it compiles components into efficient JavaScript code during the build process. Svelte does not use a virtual DOM but directly updates the DOM. The advantage of this approach is that it eliminates the need for runtime framework code, reducing application size and improving runtime efficiency.

In Svelte, the compiler analyzes your application code, smartly detecting state changes, and generates minimal code to directly manipulate the DOM. For example, if there is a state change, Svelte generates an update function that only updates the necessary DOM elements.

html
<script>
  let count = 0;

  function increment() {
    count += 1;
  }
</script>

<div>
  <p>{count}</p>
  <button on:click={increment}>Increment</button>
</div>

Summary

Overall, Solid controls component updates through a fine-grained reactive system at runtime, while Svelte directly manipulates the DOM through build-time optimizations. Solid's advantage lies in its reactive system enabling precise control over each component's updates, while Svelte's advantage is its build-time optimizations reducing runtime overhead and improving performance.