typescript-mock-builder

Zero-config CLI and library that reads a TypeScript interface and instantly generates a typed mock object or factory function — no compiler plugins, no schemas, no setup.

Install

npm install -g typescript-mock-builder
# or run directly
npx typescript-mock-builder ./src/types/User.ts

Usage

Given a TypeScript file:

// src/types/User.ts
export interface User {
  id: number;
  email: string;
  name: string;
  createdAt: Date;
  isActive: boolean;
  phone?: string;
}

Generate a plain mock object

npx typescript-mock-builder ./src/types/User.ts

Output:

const mockUser: User = {
  id: 1,
  email: '[email protected]',
  name: 'mock-name',
  createdAt: new Date(),
  isActive: false,
};

Generate a factory function

npx typescript-mock-builder ./src/types/User.ts --factory

Output:

function createUser(overrides: Partial<User> = {}): User {
  return {
    id: 1,
    email: '[email protected]',
    name: 'mock-name',
    createdAt: new Date(),
    isActive: false,
    ...overrides,
  };
}

Options

| Flag | Description | |------|-------------| | --interface <name> | Generate mock for a specific interface only | | --factory | Generate a factory function instead of a plain object | | --export | Add export keyword to the generated mock | | --var <name> | Custom variable or function name |

Examples

# Specific interface
npx typescript-mock-builder ./src/types.ts --interface Product

# With export + custom name
npx typescript-mock-builder ./src/types.ts --export --var testUser

# Factory with export
npx typescript-mock-builder ./src/types.ts --factory --export

How mock values are chosen

The generator uses name-based heuristics first, then type-based fallbacks:

| Property name pattern | Value | |-----------------------|-------| | id, *Id | 1 | | email, *Email | '[email protected]' | | url, *Url, *Uri | 'https://example.com' | | name, *Name | 'mock-<propName>' | | token, *Token | 'mock-token' | | phone, *Phone | '+1234567890' | | createdAt, updatedAt, *Date, *At | new Date() |

| Type | Value | |------|-------| | string | 'mock-<propName>' | | number | 0 | | boolean | false | | Date | new Date() | | string[], number[], T[] | [] | | Union (A \| B \| null) | picks first non-null option | | anything else | {} |

Optional properties are skipped by default.

Use as a library

import { readInterfaces, generateMock, generateMockFactory } from 'typescript-mock-builder';

const interfaces = readInterfaces('./src/types/User.ts');
const code = generateMock(interfaces[0]);
const factory = generateMockFactory(interfaces[0], { exportMock: true });

Works with type aliases too

export type Product = {
  id: number;
  name: string;
};

Type aliases that are object types are parsed the same way as interfaces.

License

MIT