TypeScript: The satisfies Operator

Core Concept

The satisfies operator validates that an expression matches a type without changing the inferred type. This is different from type annotations (:) which widen the type.

Key insight from Matt Pocock:

• "When you use a colon, the type BEATS the value"
• "When you use satisfies, the value BEATS the type"

Type Annotation vs Satisfies

type RoutingPathname = "/products" | "/cart" | "/checkout";

// Type annotation - widens to union
const url1: RoutingPathname = "/products";
// url1 is typed as: RoutingPathname (wide)