Prefer Type Annotations to Type Assertions

Overview

Type annotations (: Type) verify that values conform to types. Type assertions (as Type) tell TypeScript to trust you.

Annotations check your work. Assertions bypass checks. When you have a choice, prefer annotations.

When to Use This Skill

• Assigning values to variables
• Defining function return types
• Working with object literals
• Tempted to use as Type to fix errors
• Getting "not assignable" errors

The Iron Rule