Separation of Concerns

Overview

Each piece of code should do one thing. Data, logic, and presentation should be separate.

Mixed concerns create untestable, unreusable, unmaintainable code. Separation enables testing, reuse, and clarity.

When to Use

• Component fetches, transforms, and displays data
• Business logic mixed with UI code
• Database queries in controllers
• Hard to test a piece of code in isolation

The Iron Rule