The satisfies Operator in TypeScript

satisfies validates that an expression matches a type without widening the inferred type. It's subtly different from a type annotation.

The Problem

const config: Record<string, string | number> = {
  port: 3000,
  host: 'localhost',
}

// config.port is `string | number`, not `number` 😞

The Fix

const config = {
  port: 3000,
  host: 'localhost',
} satisfies Record<string, string | number>

// config.port is `number` ✅
// config.host is `string` ✅

When to Use

Use satisfies when you want type checking but not type widening — perfect for configuration objects, route maps, and discriminated unions.