invariant

What problem does it solve?

This Skill enhances code reliability by replacing unsafe type-only assertions with robust runtime checks, ensuring that nullable values are handled correctly and preventing runtime errors.

Core Features & Use Cases

• Safe Type Narrowing: Use invariant(value, "message") to assert that a value is not null or undefined at runtime, which also narrows its type in TypeScript.
• Avoids Non-Null Assertions: Replaces potentially dangerous ! and as operators with explicit runtime checks.
• Handles Falsy Values Correctly: Provides clear guidance on when to use invariant versus explicit guard clauses for values like 0, "", or false.
• Use Case: When fetching user data, ensure the user object is present before accessing its properties, preventing application crashes.

Quick Start

Use the invariant skill to assert that the 'user' variable is not null or undefined.