SolidJS Core Knowledge
Full Reference: See advanced.md for WebSocket primitive, context provider, chat component, room management, Socket.IO integration, and store patterns.
Deep Knowledge: Use mcp__documentation__fetch_docs with technology: solid for comprehensive documentation.
When NOT to Use This Skill
Skip this skill when:
- Working with React (use
frontend-react - APIs are different) - Building Vue applications (use
vue-composition) - Using Svelte (use
svelte) - Working with Angular (use
angular) - Need server-side only logic (no framework needed)
Component Structure
import { createSignal, createEffect, createMemo } from 'solid-js';
interface Props {
name: string;
count?: number;
}
function Counter(props: Props) {
const [localState, setLocalState] = createSignal('');
const doubled = createMemo(() => (props.count ?? 0) * 2);
createEffect(() => {
console.log('Count changed:', props.count);
});
return (
<div>
<h1>Hello {props.name}</h1>
<p>Doubled: {doubled()}</p>
<button onClick={() => setLocalState('clicked')}>
Click
</button>
</div>
);
}
Reactivity Primitives
| API | Purpose |
|---|
createSignal | Reactive state |
createMemo | Cached computation |
createEffect | Side effects |
createResource | Async data fetching |
createStore | Nested reactive objects |
Key Differences from React
- No Virtual DOM - fine-grained updates
- Props are getters - access via
props.name - No dependency arrays - auto-tracking
- Components run once - not on every render
- JSX compiles differently - expressions are reactive
Control Flow
import { Show, For, Switch, Match } from 'solid-js';
<Show when={isLoggedIn()} fallback={<Login />}>
<Dashboard />
</Show>
<For each={items()}>{(item) => <Item data={item} />}</For>
Anti-Patterns
| Anti-Pattern | Why It's Bad | Correct Approach |
|---|
| Destructuring props | Loses reactivity | Access via props.name |
| Using React patterns | Different paradigm | Use Solid primitives |
Not using <Show> component | Manual conditional logic | Use <Show when={}> |
| Recreating signals in components | Components run once | Create outside or use stores |
Using innerHTML without sanitization | XSS vulnerability | Use DOMPurify |
Not cleaning up in onCleanup | Memory leaks | Add cleanup logic |
Quick Troubleshooting
| Issue | Likely Cause | Solution |
|---|
| Props not reactive | Destructured props | Access via props.name |
| Signal not updating | Forgot to call setter | Use setCount(newValue) |
| Effect not running | Not tracking signal | Call signal inside effect: count() |
| Component re-running | Treating like React | Components run once, use signals |
| List not updating | Using array methods | Use produce() from solid-js/store |
| Memory leaks | No cleanup | Use onCleanup() |
Production Readiness
Error Handling
import { ErrorBoundary } from 'solid-js';
function App() {
return (
<ErrorBoundary
fallback={(err, reset) => (
<div>
<p>Error: {err.message}</p>
<button onClick={reset}>Retry</button>
</div>
)}
>
<MainContent />
</ErrorBoundary>
);
}
Performance
// Lazy loading components
const HeavyComponent = lazy(() => import('./HeavyComponent'));
function App() {
return (
<Suspense fallback={<Loading />}>
<HeavyComponent />
</Suspense>
);
}
// Batch updates (rarely needed)
import { batch } from 'solid-js';
batch(() => {
setCount(count() + 1);
setName('New Name');
});
Store Patterns
import { createStore, produce } from 'solid-js/store';
const [state, setState] = createStore({
users: [] as User[],
filters: { active: true },
});
// Immutable-style updates with produce
function addUser(user: User) {
setState(produce((s) => {
s.users.push(user);
}));
}
// Path-based updates
setState('users', (users) => [...users, newUser]);
setState('filters', 'active', false);
Testing
import { render, screen } from '@solidjs/testing-library';
import userEvent from '@testing-library/user-event';
import Counter from './Counter';
describe('Counter', () => {
it('increments on click', async () => {
const user = userEvent.setup();
render(() => <Counter initial={0} />);
const button = screen.getByRole('button');
await user.click(button);
expect(screen.getByText('Count: 1')).toBeInTheDocument();
});
});
Security
// innerHTML - only with trusted content
<div innerHTML={sanitizedHtml} />
// Prefer text content
<div>{userInput}</div> // Safe - auto-escaped
// XSS prevention
import DOMPurify from 'dompurify';
function SafeHtml(props: { html: string }) {
const clean = () => DOMPurify.sanitize(props.html);
return <div innerHTML={clean()} />;
}
Monitoring Metrics
| Metric | Target |
|---|
| Bundle size | < 30KB |
| First Contentful Paint | < 1s |
| Time to Interactive | < 1.5s |
| Memory usage | Stable |
Checklist
- ErrorBoundary for error handling
- Suspense for async operations
- Lazy loading for code splitting
- createStore for complex state
- Virtual lists for large data
- No innerHTML with user input
- Testing with @solidjs/testing-library
- SSR with SolidStart
- Fine-grained updates (no unnecessary re-renders)
- Bundle analysis
Reference Documentation
Deep Knowledge: Use mcp__documentation__fetch_docs with technology: solid for comprehensive documentation.