Code Design Principles

Patterns for writing clean, maintainable, and testable code.

Quick Start

// Pure function with immutability
function updateUser(user: User, age: number): User {
  return { ...user, age }; // new object, no mutation
}

Key Principles

• •Pure functions: no side effects, same input = same output
• •Immutability: create new objects/arrays instead of mutating
• •Single responsibility: one function = one task
• •Early returns: reduce nesting, improve readability
• •Composition over inheritance: inject dependencies
• •Promises over callbacks for async code
• •Template strings over concatenation
• •Plain objects for data, classes only for stateful services
• •Avoid global variables and getters/setters
• •Lazy initialization: no module-level side effects, wrap in getter functions

References

See rules.md for complete guidelines with examples.