The new TypeScript `satisfies` operator.

satisfies.ts

/* 
   The satisfies operator, introduced in TS 4.9, enforces 
   a constraint on a value without changing the inferred 
   type. It's super useful when you want to keep the most 
   specific type that can be inferred.
*/

type Data = {
  value: number | string;
};

const foo: Data = {
  value: 42,
};

// typeof foo.value is number | string (even though we *know* it's a number)

const foo = {
  value: "42",
} satisfies Data;

// typeof foo.value is now a string (the most specific type is inferred)

const foo = {
  va1ue: "42"
};

// You may be thinking, "Why even use satisfies? If I leave it off, foo.value is still a string."
// The answer: now foo has no type constaint at all. What if value is misspelled? 
// You may have noticed *it is* misspelled, but TS doesn't care. 
// However:

const foo = {
  va1ue: "42"
} satisfies Data;

// Here the TS type checker correctly stops us misspelling value.
// We get the type constraint, as well as the most specific type.
// Win-win.