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typescripttype-mapping

Check for empty type in typescript type mapping

I want to check if a type is an empty object and if thats the case map that to the void type.

type notEmpty<T> = T extends {}
? void
: T;

The above code does not work because evyr object extends the empty object.
Another approach was to turn it around:

type notEmpty2<T> = T extends { any: any }
    ? void
    : T;

But that would match only the object with the property any not any property.

Solution

  • You can also check whether T has some keys:

    type IsEmpty<T extends Record<PropertyKey, any>> =
  keyof T extends never
  ? true
  : false

type _ = IsEmpty<{}> // true
type __ = IsEmpty<{ a: number }> // false
type ___ = IsEmpty<{ a: never }> // false

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