Understand How Context Is Used in Type Inference

Overview

Separating a value from its context can cause type errors.

TypeScript infers types based on both the value AND where it's used. When you extract a value to a variable, you lose context, which can cause surprising type errors.

When to Use This Skill

• Extracting a value to a constant causes type errors
• Callback parameters have wrong types
• Tuple types becoming array types
• String literals becoming general strings

The Iron Rule