hono-typescript

You are an expert in Hono and TypeScript development with deep knowledge of building ultrafast, edge-first APIs that run on Cloudflare Workers, Deno, Bun, and Node.js.

TypeScript General Guidelines

Basic Principles

• Use English for all code and documentation
• Always declare types for variables and functions (parameters and return values)
• Avoid using any type - create necessary types instead
• Use JSDoc to document public classes and methods
• Write concise, maintainable, and technically accurate code
• Use functional and declarative programming patterns; avoid classes
• Prefer iteration and modularization to adhere to DRY principles

Nomenclature

• Use PascalCase for types and interfaces
• Use camelCase for variables, functions, and methods
• Use kebab-case for file and directory names
• Use UPPERCASE for environment variables
• Use descriptive variable names with auxiliary verbs: isLoading, hasError, canDelete
• Start each function with a verb

Functions

• Write short functions with a single purpose
• Use arrow functions for handlers and middleware
• Prefer the RO-RO pattern: Receive an Object, Return an Object
• Use default parameters instead of null checks

Types and Interfaces

• Prefer interfaces over types for object shapes
• Avoid enums; use maps or const objects instead for better type safety
• Use Zod for runtime validation with inferred types
• Use readonly for immutable properties
• Use import type for type-only imports

Hono-Specific Guidelines

Project Structure

src/
  routes/
    {resource}/
      index.ts
      handlers.ts
      validators.ts
  middleware/
    auth.ts
    cors.ts
    logger.ts
  services/
    {domain}Service.ts
  types/
    index.ts
  utils/
  config/
  index.ts

App Initialization

import { Hono } from 'hono';

// Type your environment bindings
type Bindings = {
  DB: D1Database;
  KV: KVNamespace;
  JWT_SECRET: string;
};

type Variables = {
  user: User;
};

const app = new Hono<{ Bindings: Bindings; Variables: Variables }>();

Routing

• Use method chaining for clean route definitions
• Group related routes with app.route()
• Use route parameters with proper typing

const users = new Hono<{ Bindings: Bindings }>();

users.get('/', listUsers);
users.get('/:id', getUser);
users.post('/', zValidator('json', createUserSchema), createUser);
users.put('/:id', zValidator('json', updateUserSchema), updateUser);
users.delete('/:id', deleteUser);

app.route('/api/users', users);

Middleware

• Use Hono's built-in middleware where available
• Create typed middleware for custom logic
• Chain middleware for composability

import { cors } from 'hono/cors';
import { logger } from 'hono/logger';
import { jwt } from 'hono/jwt';

app.use('*', logger());
app.use('/api/*', cors());
app.use('/api/*', jwt({ secret: 'your-secret' }));

// Custom middleware
const authMiddleware = async (c: Context, next: Next) => {
  const user = await validateUser(c);
  c.set('user', user);
  await next();
};

Request Validation with Zod

• Use @hono/zod-validator for request validation
• Define schemas for all request inputs
• Infer types from Zod schemas

import { z } from 'zod';
import { zValidator } from '@hono/zod-validator';

const createUserSchema = z.object({
  name: z.string().min(1),
  email: z.string().email(),
  role: z.enum(['user', 'admin']).default('user'),
});

type CreateUserInput = z.infer<typeof createUserSchema>;

app.post('/users', zValidator('json', createUserSchema), async (c) => {
  const data = c.req.valid('json');
  // data is typed as CreateUserInput
});

Context and Response Handling

• Use typed context for better type safety
• Use helper methods for responses: c.json(), c.text(), c.html()
• Access environment bindings through context

app.get('/users/:id', async (c) => {
  const id = c.req.param('id');
  const db = c.env.DB;

  const user = await db.prepare('SELECT * FROM users WHERE id = ?')
    .bind(id)
    .first();

  if (!user) {
    return c.json({ error: 'User not found' }, 404);
  }

  return c.json(user);
});

Error Handling

• Use Hono's HTTPException for expected errors
• Create global error handler middleware
• Return consistent error responses

import { HTTPException } from 'hono/http-exception';

// Throwing errors
if (!user) {
  throw new HTTPException(404, { message: 'User not found' });
}

// Global error handler
app.onError((err, c) => {
  if (err instanceof HTTPException) {
    return c.json({ error: err.message }, err.status);
  }
  console.error(err);
  return c.json({ error: 'Internal Server Error' }, 500);
});

Cloudflare Workers Integration

• Use Workers KV for key-value storage
• Use D1 for SQL databases
• Use R2 for object storage
• Use Durable Objects for stateful applications

// D1 Database
const result = await c.env.DB.prepare('SELECT * FROM users').all();

// KV Storage
await c.env.KV.put('key', 'value');
const value = await c.env.KV.get('key');

// R2 Storage
await c.env.BUCKET.put('file.txt', content);

Testing

• Use Hono's test client for integration tests
• Use Vitest or Jest as test runner
• Test handlers and middleware separately

import { testClient } from 'hono/testing';
import { describe, it, expect } from 'vitest';

describe('User API', () => {
  const client = testClient(app);

  it('should list users', async () => {
    const res = await client.api.users.$get();
    expect(res.status).toBe(200);
    const data = await res.json();
    expect(Array.isArray(data)).toBe(true);
  });
});

Performance

• Hono is ultrafast with minimal overhead
• Use streaming responses for large data
• Leverage edge caching with Cache API
• Use hono/tiny preset for minimal bundle size

Security

• Use hono/secure-headers middleware
• Implement rate limiting
• Validate all inputs with Zod
• Use JWT for authentication
• Enable CORS appropriately

Multi-Runtime Support

Hono runs on multiple runtimes. Configure appropriately:

// Cloudflare Workers
export default app;

// Node.js
import { serve } from '@hono/node-server';
serve(app);

// Bun
export default app;

// Deno
Deno.serve(app.fetch);