TypeScript の satisfies ってなんだよ

code:ts

type User = { email: string };

// ⭕: { email: string } 型

const jane = { email: "jane@example.com" } satisfies User;

// ❌: Object literal may only specify known properties, and 'id' does not exist in type 'User'.

const john = { email: "john@example.com", id: 1 } satisfies User;

// annotation: User 型

const taro: User = { email: "taro@example.com" };

オブジェクトのキーが充足しているかをチェック

型推論を残して型の可読性を高める

オブジェクトのキーが充足しているかをチェック

code:ts

type Color = "red" | "green" | "blue";

const palette = {

green: "#00ff00",

blue: "#0000ff",

} satisfies Record<Color, unknown>;

const wip_palette = {

green: "#00ff00",

blue: "#0000ff",

} satisfies Record<Color, unknown>;

const asserted_palette = {

green: "#00ff00",

blue: "#0000ff",

} as Record<Color, unknown>;