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Type Safety

End-to-end type safety from request validation to response serialization. TypeScript automatically knows what properties are available—no guessing, no runtime errors.

On this page

Types Inferred Automatically

Define your schema once. Get runtime validation and compile-time types.
TypeScript automatically knows what's available.

It Just Works

Define once, get both validation and types

typescript

1import { createApp } from '@morojs/moro';
2import { z } from 'zod';
3
4const CreateUserSchema = z.object({
5  name: z.string().min(1),
6  email: z.string().email(),
7  age: z.number().min(18)
8});
9
10app.post('/users', {
11  body: CreateUserSchema,
12  handler: ({ body }) => {
13    // TypeScript automatically knows:
14    // body.name: string
15    // body.email: string
16    // body.age: number
17    
18    // No type assertions needed!
19    return { success: true, user: body };
20  }
21});

Why Type Safety Matters

Catch errors at compile time, not in production. Get IntelliSense everywhere.

Without type safety, you're guessing property names and hoping the API returns what you expect.

Without Types

  • •Guessing property names
  • •Runtime errors in production
  • •No autocomplete or IntelliSense
  • •Manual type checking everywhere

With MoroJS

  • •Automatic type inference
  • •Errors caught at compile time
  • •Full IntelliSense support
  • •TypeScript knows what's available

It's This Easy

Define a schema. Get types automatically. That's it.

Automatic type inference from schemas

typescript

1// Define schema
2const UserSchema = z.object({
3  name: z.string(),
4  email: z.string().email()
5});
6
7// Use in route - types are automatic!
8app.post('/users', {
9  body: UserSchema,
10  handler: ({ body }) => {
11    // body is fully typed!
12    return { user: body };
13  }
14});

Why It Makes Sense

Catch Errors Early

TypeScript catches errors before your code runs. No more production surprises.

Better DX

Full autocomplete and IntelliSense. Write code faster with confidence.

Self-Documenting

Types serve as documentation. See what's available without reading docs.

How It Works

MoroJS automatically infers types from your route patterns, validation schemas, and middleware context. You define your data structure once, and TypeScript knows about it everywhere.

Request Type Safety

Route parameters, query strings, and request bodies are automatically typed based on your route patterns and schemas.

Automatic Parameter Type Inference

typescript

1import { createApp } from '@morojs/moro';
2
3const app = createApp();
4
5// Parameters are automatically typed as strings
6app.get('/users/:userId/posts/:postId', ({ params }) => {
7  // params.userId: string
8  // params.postId: string
9  console.log(params.userId); // ✅ TypeScript knows this is a string
10  console.log(params.nonExistent); // ❌ TypeScript error
11  
12  return { userId: params.userId, postId: params.postId };
13});

Query Parameter Types

typescript

1app.get('/search', ({ query }) => {
2  // All query parameters are automatically available
3  // query.q: string | undefined
4  // query.limit: string | undefined
5  // query.page: string | undefined
6  
7  const searchTerm = query.q || '';
8  const limit = parseInt(query.limit || '10');
9  const page = parseInt(query.page || '1');
10  
11  return { searchTerm, limit, page };
12});

Schema-Based Request Body Validation

typescript

1import { createApp } from '@morojs/moro';
2import { z } from 'zod';
3
4const CreateUserSchema = z.object({
5  name: z.string().min(1).max(100),
6  email: z.string().email(),
7  age: z.number().min(18).max(120),
8  role: z.enum(['user', 'admin']).default('user')
9});
10
11app.post('/users', {
12  body: CreateUserSchema,
13  handler: ({ body }) => {
14    // body is fully typed and validated!
15    // body.name: string
16    // body.email: string  
17    // body.age: number
18    // body.role: 'user' | 'admin'
19    
20    console.log(`Creating user: ${body.name}`);
21    
22    // TypeScript prevents you from accessing invalid properties
23    // console.log(body.invalidProp); // ❌ TypeScript error
24    
25    return { success: true, user: body };
26  }
27});

Parameter Validation

typescript

1const UserParamsSchema = z.object({
2  userId: z.string().uuid()
3});
4
5app.get('/users/:userId', {
6  params: UserParamsSchema,
7  handler: ({ params }) => {
8    // params.userId: string (validated as UUID)
9    // TypeScript knows it's a valid UUID string
10    return { userId: params.userId };
11  }
12});

Response Type Safety

Define response schemas to ensure your API returns consistent data. TypeScript ensures your responses match the schema.

Response Schema Definition

typescript

1const UserResponseSchema = z.object({
2  id: z.string().uuid(),
3  name: z.string(),
4  email: z.string().email(),
5  role: z.enum(['user', 'admin']),
6  createdAt: z.string().datetime(),
7  updatedAt: z.string().datetime()
8});
9
10const ErrorResponseSchema = z.object({
11  error: z.string(),
12  message: z.string(),
13  code: z.number()
14});
15
16app.get('/users/:userId', {
17  params: UserParamsSchema,
18  response: {
19    200: UserResponseSchema,
20    404: ErrorResponseSchema,
21    500: ErrorResponseSchema
22  },
23  handler: async ({ params }) => {
24    const user = await getUserById(params.userId);
25    
26    if (!user) {
27      // TypeScript ensures this matches ErrorResponseSchema
28      return {
29        status: 404,
30        body: {
31          error: 'NOT_FOUND',
32          message: 'User not found',
33          code: 404
34        }
35      };
36    }
37    
38    // TypeScript ensures this matches UserResponseSchema
39    return {
40      status: 200,
41      body: {
42        id: user.id,
43        name: user.name,
44        email: user.email,
45        role: user.role,
46        createdAt: user.createdAt.toISOString(),
47        updatedAt: user.updatedAt.toISOString()
48      }
49    };
50  }
51});

Context Type Safety

Middleware can add typed data to the request context. TypeScript knows what's available in your handlers.

Typed Middleware Context

typescript

1// Define types for your context
2interface AuthContext {
3  user: {
4    id: string;
5    email: string;
6    role: 'user' | 'admin';
7  };
8}
9
10const authMiddleware = async ({ headers }): Promise<AuthContext> => {
11  const token = headers.authorization?.replace('Bearer ', '');
12  if (!token) {
13    throw new Error('No token provided');
14  }
15  
16  const user = await verifyToken(token);
17  return { user };
18};
19
20app.get('/profile', {
21  middleware: [authMiddleware],
22  handler: ({ context }) => {
23    // context.user is fully typed!
24    // context.user.id: string
25    // context.user.email: string
26    // context.user.role: 'user' | 'admin'
27    
28    return {
29      profile: {
30        id: context.user.id,
31        email: context.user.email,
32        role: context.user.role
33      }
34    };
35  }
36});

Advanced Type Patterns

Branded Types for Better Safety

typescript

1// Create branded types for different ID types
2type UserId = string & { readonly brand: unique symbol };
3type PostId = string & { readonly brand: unique symbol };
4
5const UserIdSchema = z.string().uuid().transform((val) => val as UserId);
6const PostIdSchema = z.string().uuid().transform((val) => val as PostId);
7
8app.get('/users/:userId/posts/:postId', {
9  params: z.object({
10    userId: UserIdSchema,
11    postId: PostIdSchema
12  }),
13  handler: ({ params }) => {
14    // params.userId: UserId (not just string)
15    // params.postId: PostId (not just string)
16    
17    // TypeScript prevents mixing up different ID types
18    const post = getPost(params.postId, params.userId); // ✅ Correct order
19    // const post = getPost(params.userId, params.postId); // ❌ Type error
20    
21    return { post };
22  }
23});

Conditional Response Types

typescript

1const PaginatedResponseSchema = <T extends z.ZodType>(itemSchema: T) =>
2  z.object({
3    data: z.array(itemSchema),
4    pagination: z.object({
5      page: z.number(),
6      limit: z.number(),
7      total: z.number(),
8      hasMore: z.boolean()
9    })
10  });
11
12app.get('/users', {
13  query: z.object({
14    page: z.coerce.number().default(1),
15    limit: z.coerce.number().min(1).max(100).default(20)
16  }),
17  response: {
18    200: PaginatedResponseSchema(UserResponseSchema)
19  },
20  handler: async ({ query }) => {
21    const users = await getUsers(query.page, query.limit);
22    const total = await getUserCount();
23    
24    return {
25      data: users,
26      pagination: {
27        page: query.page,
28        limit: query.limit,
29        total,
30        hasMore: (query.page * query.limit) < total
31      }
32    };
33  }
34});

Best Practices

Do

  • • Define schemas for all inputs and outputs
  • • Use strict TypeScript configuration
  • • Leverage z.infer for type extraction
  • • Create reusable schema components
  • • Use branded types for IDs
  • • Document complex types with JSDoc

Don't

  • • Use 'any' types
  • • Skip validation for external data
  • • Ignore TypeScript errors
  • • Mix validated and unvalidated data
  • • Use type assertions without validation
  • • Forget to handle all response cases

Next Steps

Validation Guide

Deep dive into Zod schemas and validation patterns

Response Patterns

Learn about standardized response formats

Intelligent Routing

See how routing works with type safety