🔍 type-thief

Automatically generate TypeScript types from your runtime data with zero effort! Perfect for creating type definitions from API responses without writing them manually.

🌟 Why type-thief?

Tired of manually creating TypeScript interfaces for your API responses? type-thief solves this problem by automatically generating accurate type definitions from your runtime data:

• ✅ Save time - No more tedious manual type creation
• ✅ Stay in sync - Types always match your actual API responses
• ✅ Zero dependencies - Lightweight addition to your project
• ✅ Smart type inference - Handles nested objects, arrays, and relationships

⚡ Quick Start

import { thief } from 'type-thief';

// Generate a type from a simple object
const user = { name: 'John', age: 30 };
thief(user, { typeName: 'User', fileName: 'user.ts' });

// Result in types/user.ts:
// export type User = { name: string; age: number };

🚀 Next.js Example: Todo App

Here's how to use Type Thief in a Next.js application to generate types for your API data:

// app/page.tsx
import { thief } from 'type-thief';

async function getTodos() {
  // Fetch a single todo first
  const singleRes = await fetch('https://jsonplaceholder.typicode.com/todos/1');
  const singleTodo = await singleRes.json();
  
  // Generate the Todo type
  await thief(singleTodo, {
    typeName: 'Todo',
    outputDir: 'types',
    fileName: 'todo.ts',
    debug: true
  });
  
  // Then fetch all todos
  const todosRes = await fetch('https://jsonplaceholder.typicode.com/todos');
  const todos = await todosRes.json();
  
  // Generate the Todos type - it will automatically use Todo[] if structures match
  await thief(todos, {
    typeName: 'Todos',
    outputDir: 'types',
    fileName: 'todo.ts',
    debug: true
  });
  
  return todos;
}

export default async function Home() {
  const todos = await getTodos();

  return (
    <main className="p-8">
      <h1 className="text-2xl font-bold mb-4">Todos</h1>
      <ul className="space-y-2">
        {todos.slice(0, 5).map((todo) => (
          <li key={todo.id} className="p-4 border rounded">
            <span className={`${todo.completed ? 'line-through text-green-600' : 'text-red-600'}`}>
              {todo.title}
            </span>
          </li>
        ))}
      </ul>
    </main>
  );
}

This will generate the following types in types/todo.ts:

export type Todo = {
  userId: number;
  id: number;
  title: string;
  completed: boolean;
};

export type Todos = Todo[];

Notice how the Todos type automatically references the existing Todo type instead of duplicating the structure!

💡 Common Use Cases

• API Integration: Generate types from REST or GraphQL API responses
• Backend Communication: Keep frontend types in sync with your backend data
• Prototyping: Quickly build type-safe applications without writing types manually
• Data Exploration: Understand the structure of complex data by generating types

🛠️ Options

| Option | Type | Default | Description | |--------|------|---------|-------------| | typeName | string | 'GeneratedType' | Name of the generated type | | outputDir | string | 'types' | Directory where type files are saved | | fileName | string | 'generated.ts' | Name of the output file | | debug | boolean | false | Enable debug logging |

✨ Features

• 🔄 Automatically detects arrays and generates appropriate types
• 🧩 Reuses existing types when possible
• 📝 Preserves existing type definitions
• 🔍 Smart type inference for nested objects and arrays
• 🌟 Special handling for common patterns like Todo/Todos
• 📦 Zero dependencies - lightweight and fast

📦 Installation

npm install type-thief
# or
yarn add type-thief
# or
pnpm add type-thief