Overview

npm install eslint-plugin-modularity --save-dev

// eslint.config.js
import modularity from 'eslint-plugin-modularity';

export default [
  modularity.configs.recommended,

  // Apply strict DDD enforcement to domain layer
  {
    files: ['src/domain/**/*.ts'],
    ...modularity.configs.strict,
  },
];

// ❌ Bad: Anemic model, no behavior
class Order {
  id: string;
  items: OrderItem[];
  status: OrderStatus;
}

// ✅ Good: Rich domain model with behavior
class Order {
  id: string;
  private items: OrderItem[];
  private status: OrderStatus;

  addItem(item: OrderItem): void {
    /* ... */
  }
  submit(): void {
    /* ... */
  }
  cancel(reason: string): void {
    /* ... */
  }
}

// ❌ Bad: Mutable value object
class Money {
  amount: number; // Can be mutated!
}

// ✅ Good: Immutable value object
class Money {
  readonly amount: number;
  readonly currency: string;

  add(other: Money): Money {
    return new Money(this.amount + other.amount, this.currency);
  }
}

// ❌ Bad: Utils with external dependencies
// src/utils/formatters.ts
import axios from 'axios';

export async function fetchAndFormat(id: string) {
  const data = await axios.get(`/api/${id}`); // External API call!
  return format(data);
}

// ✅ Good: Pure utility function
export function format(data: Data): FormattedData {
  return {
    /* pure transformation */
  };
}