Use readonly to Avoid Errors Associated with Mutation

Overview

readonly signals intent and lets TypeScript catch accidental mutations.

Mutation is a common source of bugs. readonly helps TypeScript catch them at compile time and documents your intent to other developers.

When to Use This Skill

• Passing arrays or objects to functions
• Debugging unexpected data changes
• Designing function signatures
• Working with shared state
• Creating APIs that shouldn't mutate inputs

The Iron Rule