Typescript Best Practices

TypeScript Best Practices

Priority: P1 (OPERATIONAL)

Idiomatic patterns for writing clean, maintainable TypeScript code.

Implementation Guidelines

• Naming Conventions:
  • PascalCase for classes, interfaces, types, enums
  • camelCase for variables, functions, methods, parameters
  • UPPER_SNAKE_CASE for constants
  • Prefix interfaces with I only when necessary for disambiguation
• Functions:
  • Prefer arrow functions for callbacks and short functions
  • Use regular functions for methods and exported functions
  • Always specify return types for public APIs
• Modules:
  • One export per file for major components/classes
  • Use named exports over default exports for better refactoring
  • Organize imports: external -> internal -> relative
• Async/Await:
  • Prefer async/await over raw Promises
  • Always handle errors with try/catch in async functions
  • Use Promise.all() for parallel operations
• Classes:
  • Use private/protected/public modifiers explicitly
  • Prefer composition over inheritance
  • Use readonly for properties that don't change after construction
• Exhaustiveness Checking: Use never type in switch cases.
• Assertion Functions: Use asserts for runtime type validation.
• Optional Properties: Use ?:, not | undefined.
• Type Imports: Use import type for tree-shaking.

Anti-Patterns

• No Default Exports: Use named exports.
• No Implicit Returns: Specify return types.
• No Unused Variables: Enable noUnusedLocals.
• No require: Use ES6 import.
• No Empty Interfaces: Use type or non-empty interface.

Code

// Named Export + Immutable Interface
export interface User {
  readonly id: string;
  name: string;
}

// Exhaustive Check
function getStatus(s: 'ok' | 'fail') {
  switch (s) {
    case 'ok': return 'OK';
    case 'fail': return 'Fail';
    default: const _chk: never = s; return _chk;
  }
}

// Assertion
function assertDefined<T>(val: T): asserts val is NonNullable<T> {
  if (val == null) throw new Error("Defined expected");
}
```  private readonly repository: UserRepository;

  constructor(repository: UserRepository) {
    this.repository = repository;
  }

  async getUser(id: string): Promise<UserProfile> {
    try {
      return await this.repository.findById(id);
    } catch (error) {
      throw new Error(`Failed to get user: ${error.message}`);
    }
  }
}

// Organize imports
import { Injectable } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';

import { UserRepository } from '@/repositories/user.repository';
import { Logger } from '@/utils/logger';

// Type-only imports
import type { Request, Response } from 'express';

Reference & Examples

For project structure and module organization: See references/REFERENCE.md.

Related Topics

language | tooling | security

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