The satisfies Operator in TypeScript

The satisfies Operator

What is satisfies?

Introduced in TypeScript 4.9, satisfies lets you validate that an expression matches a type without changing its inferred type.

Basic Usage

// Without satisfies — type widens
const palette = {
  red: [255, 0, 0],
  green: [0, 255, 0],
  blue: [0, 0, 255],
};
// palette.red is number[] — lost tuple type

// With satisfies — validates + preserves literal type
const palette = {
  red: [255, 0, 0],
  green: [0, 255, 0],
  blue: [0, 0, 255],
} satisfies Record<string, [number, number, number]>;
// palette.red is [number, number, number] — preserved!

Real Project Example

// Color palette with validation
const colors = {
  primary: "#6366f1",
  secondary: "#a78bfa",
  success: "#22c55e",
  danger: "#ef4444",
} satisfies Record<string, `#${string}`>;

// All values validated as hex colors
// But each key still has its literal type

Interview Questions

Easy: What does the satisfies operator do?

Medium: How is satisfies different from a type annotation?

Hard: When would you choose satisfies over a type assertion?