javascript-typescript.md
3,1 KB • MD • jun. 18, 2026 06:54
---
name: javascript-typescript
description: JavaScript and TypeScript development with ES6+, Node.js, React, and modern web frameworks. Use for frontend, backend, or full-stack JavaScript/TypeScript projects.
source: wshobson/agents
license: MIT
---
# JavaScript/TypeScript Development
## TypeScript Configuration
```json
{
"compilerOptions": {
"target": "ES2022",
"module": "ESNext",
"moduleResolution": "bundler",
"strict": true,
"noUncheckedIndexedAccess": true,
"noImplicitOverride": true,
"skipLibCheck": true,
"declaration": true,
"outDir": "./dist"
},
"include": ["src/**/*"],
"exclude": ["node_modules", "dist"]
}
```
## Type Patterns
### Utility Types
```typescript
// Pick specific properties
type UserPreview = Pick<User, 'id' | 'name'>;
// Omit properties
type CreateUser = Omit<User, 'id' | 'createdAt'>;
// Make all properties optional
type PartialUser = Partial<User>;
// Make all properties required
type RequiredUser = Required<User>;
// Extract union types
type Status = 'pending' | 'active' | 'inactive';
type ActiveStatus = Extract<Status, 'active' | 'pending'>;
```
### Discriminated Unions
```typescript
type Result<T> =
| { success: true; data: T }
| { success: false; error: Error };
function handleResult<T>(result: Result<T>) {
if (result.success) {
console.log(result.data); // T
} else {
console.error(result.error); // Error
}
}
```
### Generic Constraints
```typescript
interface HasId {
id: string | number;
}
function findById<T extends HasId>(items: T[], id: T['id']): T | undefined {
return items.find(item => item.id === id);
}
```
## Modern JavaScript
### Destructuring & Spread
```javascript
const { name, ...rest } = user;
const merged = { ...defaults, ...options };
const [first, ...others] = items;
```
### Optional Chaining & Nullish Coalescing
```javascript
const city = user?.address?.city ?? 'Unknown';
const count = data?.items?.length ?? 0;
```
### Array Methods
```javascript
const adults = users.filter(u => u.age >= 18);
const names = users.map(u => u.name);
const total = items.reduce((sum, item) => sum + item.price, 0);
const hasAdmin = users.some(u => u.role === 'admin');
const allActive = users.every(u => u.active);
```
## React Patterns
```typescript
// Props with children
interface CardProps {
title: string;
children: React.ReactNode;
}
// Event handlers
interface ButtonProps {
onClick: (event: React.MouseEvent<HTMLButtonElement>) => void;
}
// Custom hooks
function useLocalStorage<T>(key: string, initial: T) {
const [value, setValue] = useState<T>(() => {
const stored = localStorage.getItem(key);
return stored ? JSON.parse(stored) : initial;
});
useEffect(() => {
localStorage.setItem(key, JSON.stringify(value));
}, [key, value]);
return [value, setValue] as const;
}
```
## Node.js Patterns
```typescript
// ES Modules
import { readFile } from 'node:fs/promises';
import { join } from 'node:path';
// Error handling
process.on('unhandledRejection', (reason) => {
console.error('Unhandled Rejection:', reason);
process.exit(1);
});
```