04 — Type Inference & Annotations

Core Concepts

• Type Inference — TypeScript automatically determines types from values
• Explicit Annotations — manually specifying types with : Type syntax
• Contextual Typing — type inferred from where the expression appears (callbacks, etc.)
• const Assertions — as const narrows to the most specific (literal) type
• satisfies Operator — validates type compatibility without widening (TS 5.0+)
• Return Type Inference — functions infer return types from return statements
• Best Common Type — TS picks the best type that fits all array elements

When to Annotate vs Infer