JS Boundaries provides a powerful architectural enforcement solution for JavaScript and TypeScript projects through an ESLint plugin. Created by Javier Brea, the project aims to help developers maintain clean, scalable, and manageable codebases by enabling them to draw and enforce architectural boundaries. By defining clear rules for how different parts of a project should interact, it prevents unwanted coupling and ensures that architectural patterns are consistently followed, reducing technical debt over time.

The functionality revolves around analyzing the folder and file structure of a project to classify dependencies. The plugin intercepts import, require, and export statements to understand relationships between files based on their location and role. By assigning metadata to these dependencies—such as type, category, and source—the plugin allows developers to define complex interaction rules. It provides instant feedback within IDEs and can be integrated into CI/CD pipelines to block builds that violate established architectural constraints.

Some of the key features are:

• Element Definition: Easily categorize files into components, services, or layers using file patterns.
• Dependency Rules: Enforce complex allow/disallow rules between different architectural elements.
• Instant Feedback: Receive immediate ESLint errors when architectural boundaries are breached.
• Advanced Analysis: Beyond standard imports, it supports require, exports, and dynamic import statements.
• TypeScript Support: Native integration with TypeScript, including path mapping and full type definitions.
• Extensible Configuration: Customize dependency analysis through flexible global settings and configuration helpers.
• Architectural Validation: Ensure clean architecture principles like separating controllers from models and views are rigorously maintained.

The tool is designed to work as an ESLint plugin that developers add to their project's development dependencies. Once installed, the configuration is managed within the ESLint config file. Developers define element descriptors that map file patterns to architectural types, then set dependency rules using selectors that specify allowed interactions. The plugin automatically monitors the dependency graph, providing a runtime-like analysis during linting that gives developers clear, actionable information about where violations occur.

Some common use cases include:

• Clean Architecture Implementation: Enforcing strict boundaries between domain layers, service layers, and UI components.
• Dependency Management: Preventing low-level utility files or models from accidentally importing higher-level view components.
• Monorepo Scaling: Maintaining consistent architectural patterns across multiple packages within a single workspace.
• Codebase Cleanup: Identifying and resolving unauthorized coupling in large, legacy codebases by incrementally defining and enforcing boundaries.
• Team Guardrails: Preventing developers from introducing new, unauthorized dependencies that violate project structure guidelines.