TypeScript has no general type that guarantees a value has exactly zero properties. The familiar {} type does not mean “empty object”: with strictNullChecks enabled, it accepts any non-nullish value, including strings and numbers. Choose a type for the constraint you actually need, and validate at runtime if true emptiness matters.
What does {} mean in TypeScript?
With strictNullChecks enabled, {} accepts every value except null and undefined. It accepts both primitives and objects:
const text: {} = "hello";
const data: {} = { extra: true };So {} is not a type for an object with zero properties. The TypeScript project FAQ explains that TypeScript has no sealed or closed types and therefore no type that refers to values with zero properties: TypeScript FAQ: “Primitives are {}, and {} Doesn’t Mean object”.
When strictNullChecks is disabled, nullability behavior differs, so avoid relying on the non-nullish interpretation across configurations. The Handbook recommends strict null checking and discusses its effect in Basic Types.
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Which type should you use instead?
Pick according to what the value may be and what you need to do with it:
| Intended constraint | Starting type | What it does not guarantee |
|---|---|---|
Any value except null or undefined |
{} |
It also accepts primitives; it does not mean empty object. |
| Any non-primitive value | object |
It permits properties, arrays, and functions. |
| Arbitrary input you have not inspected | unknown |
You must narrow it before using it as a more specific type. |
| A known configuration shape | A named type or interface | Structural typing does not generally rule out extra properties. |
| No own enumerable string-keyed properties at runtime | A runtime check | You must decide how to treat symbols, inherited properties, and non-enumerable properties. |
Use object to exclude primitives
The object type accepts non-primitive values, but it does not forbid properties. For example, an object with an extra property is assignable to object, while a string is not:
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const value: object = { extra: true };
// const text: object = "hello"; // ErrorArrays and functions are objects in this sense too. See the Handbook’s Basic Types discussion.
Use unknown for uninspected input
unknown can hold any value, including nullish values. Unlike any, it requires you to check or narrow the value before treating it as an object or accessing its properties:
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function inspect(value: unknown) {
if (typeof value === "object" && value !== null && !Array.isArray(value)) {
// The value is object-like, but its properties are not yet known.
}
}The narrowing requirement is what makes unknown useful at boundaries where external data has not yet been validated. The Handbook covers it in Basic Types.
Use a named type for a meaningful shape
If a value has a known purpose, describe its permitted properties directly:
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type Options = {
mode?: "fast" | "safe";
};This type describes the declared configuration shape; it is not a universal guarantee that no other properties can exist. TypeScript’s object types are structural, as explained in the Handbook’s Object Types.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Do excess-property checks make an object type exact?
No. TypeScript may flag an undeclared property when you assign a fresh object literal directly to a named type. This excess-property check helps catch mistakes such as misspelled option names, but it is a diagnostic for that assignment context—not a general sealed-object guarantee.
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type Options = { mode?: "fast" | "safe" };
const options: Options = { mode: "fast", extra: true }; // Excess-property errorThe fact that this fresh literal is rejected does not mean every value assignable to Options is guaranteed to have no other properties. The Handbook explains excess-property checks in Object Types; the FAQ describes the broader absence of sealed types in its section on why {} does not refer to objects with no properties.
Does Record<string, never> define an empty object?
It is not the general empty-object type to reach for. Record<Keys, Type> is a mapped utility type for describing properties from a selected key set, such as a dictionary; it is not a switch that makes object types exact. The Handbook documents Record in Utility Types, and the TypeScript FAQ cautions against treating such a suggestion as a sealed type.
How can you check that a value is empty at runtime?
First decide what “empty” means for your application. This function checks that a value is a non-null object, excludes arrays, and has no own enumerable string-keyed properties:
function hasNoEnumerableStringKeys(value: unknown): boolean {
return typeof value === "object" &&
value !== null &&
!Array.isArray(value) &&
Object.keys(value).length === 0;
}Object.keys does not count symbol keys, inherited properties, or non-enumerable properties. If any of those matter, add checks that match the application’s definition of empty. Runtime validation answers a question about a concrete value; it does not create a compile-time exact-object type.
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Historically, unconstrained generic type parameters had an implicit {} constraint. TypeScript 3.5 changed that implicit constraint to unknown. This matters when reading older generic code: an unconstrained type parameter should not be understood as an empty object. The change is documented in the TypeScript Wiki’s Breaking Changes.
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