API Typegen

A TypeScript type generator that creates type definitions from API endpoint responses. Ideal for APIs that don't provide OpenAPI (Swagger) specifications.

Example

Input (config.json):

{
  "endpoints": [
    {
      "typeName": "Todo",
      "url": "https://jsonplaceholder.typicode.com/todos/1",
      "method": "GET"
    },
    {
      "typeName": "Posts",
      "url": "https://jsonplaceholder.typicode.com/posts",
      "method": "GET"
    },
    {
      "typeName": "User",
      "url": "https://jsonplaceholder.typicode.com/users",
      "method": "POST",
      "headers": {
        "Content-Type": "application/json"
      },
      "body": {
        "name": "John Doe",
        "email": "johndoe@example.com"
      }
    }
  ]
}

Output (types.ts):

export interface Todo {
  userId?: number;
  id?: number;
  title?: string;
  completed?: boolean;
}

export interface PostsItem {
  userId?: number;
  id?: number;
  title?: string;
  body?: string;
}
export type Posts = PostsItem[];

export interface User {
  name?: string;
  email?: string;
  id?: number;
}

Installation

npm install api-typegen

Usage

CLI

You can use API Typegen directly from the command line:

npx api-typegen --config path/to/config.json --output types.ts

Programmatic Usage

You can also use API Typegen programmatically:

import fs from "fs";
import { generateTypes, type Endpoint } from "api-typegen";

const main = async () => {
  const endpoints: Endpoint[] = [
    {
      typeName: "Todo",
      url: "https://jsonplaceholder.typicode.com/todos/1",
      method: "GET",
    },
    {
      typeName: "Posts",
      url: "https://jsonplaceholder.typicode.com/posts",
      method: "GET",
    },
    {
      typeName: "User",
      url: "https://jsonplaceholder.typicode.com/users",
      method: "POST",
      headers: {
        "Content-Type": "application/json",
      },
      body: {
        name: "John Doe",
        email: "johndoe@example.com",
      },
    },
  ];

  const types = await generateTypes(endpoints);
  fs.writeFileSync("exampleTypes.ts", types);
};

main();

Configuration

Each endpoint in the configuration can have the following properties:

• typeName (required): The name of the generated TypeScript type.

• url (required): The URL of the API endpoint.

• method (required): The HTTP method (GET, POST, PUT, DELETE, PATCH).

• headers (optional): An object of custom headers to send with the request.

• queryParams (optional): An object of query parameters to append to the URL.

• body (optional): The request body for POST, PUT, or PATCH requests.

• override (optional): A JSON Schema object to override the inferred schema.

Schema Override

You can override a type by providing a JSON Schema object in the override property. This allows you to customize the generated types to better suit your needs. For example, the following configuration makes all the properties in Todo no longer optional and the completed property nullable:

{
  "endpoints": [
    {
      "typeName": "Todo",
      "url": "https://jsonplaceholder.typicode.com/todos/1",
      "method": "GET",
      "override": {
        "properties": {
          "completed": { "type": ["boolean", "null"] }
        },
        "required": ["userId", "id", "title", "completed"]
      }
    }
  ]
}

Output:

export interface Todo {
  userId: number;
  id: number;
  title: string;
  completed: boolean | null;
}