Modern API design has evolved far beyond simple CRUD operations. Today’s applications require APIs that are resilient, scalable, and developer-friendly while supporting diverse client needs and complex business workflows. This guide explores proven patterns that address these challenges.

Foundational Design Principles

API-First Development

Design your API before implementation to ensure consistency and usability:

// Define API contract first
interface UserAPI {
  // Resource operations
  getUser(id: string): Promise<User>;
  updateUser(id: string, updates: Partial<User>): Promise<User>;
  deleteUser(id: string): Promise<void>;
  
  // Collection operations
  listUsers(filters: UserFilters, pagination: Pagination): Promise<PagedResult<User>>;
  searchUsers(query: SearchQuery): Promise<SearchResult<User>>;
  
  // Business operations
  activateUser(id: string): Promise<User>;
  deactivateUser(id: string): Promise<User>;
  resetUserPassword(id: string): Promise<void>;
}

// OpenAPI specification (generated or hand-written)
const userAPISpec = {
  openapi: '3.0.0',
  info: {
    title: 'User Management API',
    version: '1.0.0'
  },
  paths: {
    '/users/{id}': {
      get: {
        summary: 'Get user by ID',
        parameters: [
          {
            name: 'id',
            in: 'path',
            required: true,
            schema: { type: 'string', format: 'uuid' }
          }
        ],
        responses: {
          200: {
            description: 'User found',
            content: {
              'application/json': {
                schema: { $ref: '#/components/schemas/User' }
              }
            }
          },
          404: {
            description: 'User not found',
            content: {
              'application/json': {
                schema: { $ref: '#/components/schemas/Error' }
              }
            }
          }
        }
      }
    }
  }
};

Resource-Oriented Design

Structure APIs around resources, not actions:

Code quality gates serve as automated checkpoints that prevent substandard code from progressing through your development pipeline. When implemented effectively, they maintain consistent standards across teams while accelerating development by catching issues early and reducing manual review overhead.

Understanding Quality Gates

Quality gates are automated checks that evaluate code against predefined criteria before allowing it to proceed to the next stage of development. Unlike simple linting, quality gates encompass comprehensive analysis including code coverage, complexity metrics, security vulnerabilities, and architectural compliance.

Test-Driven Development (TDD) has evolved significantly with modern TypeScript tooling and frameworks. While most developers understand the basic red-green-refactor cycle, mastering TDD in TypeScript requires understanding advanced patterns, effective mocking strategies, and leveraging the type system for better test design.

Beyond Basic TDD: Advanced Patterns

Type-Driven Test Design

TypeScript’s type system provides unique opportunities to improve test design. Instead of just testing implementation details, we can use types to guide our test structure and ensure comprehensive coverage: