02 — Primitive Types & Special Types

Core Concepts

• string, number, boolean — the three most common primitives
• any — disables type checking entirely; avoid it
• unknown — type-safe alternative to any; must narrow before use
• void — function returns nothing (undefined implicitly)
• never — function never returns (throws or infinite loop)
• null / undefined — distinct types when strictNullChecks is on
• bigint — arbitrary precision integers (100n)
• symbol — unique identifiers (Symbol("key"))
• literal types — exact values as types ("hello", 42, true)

any vs unknown

When to Use

• unknown over any — always; narrow with typeof / instanceof
• never in exhaustive switch checks and unreachable code
• void for callback return types you don't care about
• literal types for strict string/number values (status codes, roles)