Typescript check for the ‘any’ type

by

Yeah, you can test for any:

type IfAny<T, Y, N> = 0 extends (1 & T) ? Y : N; 
type IsAny<T> = IfAny<T, true, never>;
type A = IsAny<any> // true
type B = IsAny<number> // never
type C = IsAny<unknown> // never
type D = IsAny<never> // never

The explanation for this is in this answer. In short, any is intentionally unsound, and violates the normal rules of types. You can detect this violation because it lets you do something crazy like assign 0 to 1.

More Related Contents:

  1. Interfaces vs Types in TypeScript
  2. Why does A | B allow a combination of both, and how can I prevent it?
  3. How to return value from function which has Observable subscription inside?
  4. Create an enum with string values
  5. Typescript: TS7006: Parameter ‘xxx’ implicitly has an ‘any’ type
  6. Parameters generic of overloaded function doesn’t contain all options
  7. Enforcing the type of the indexed members of a Typescript object?
  8. Constructor overload in TypeScript
  9. Typescript: Can I define an n-length tuple type?
  10. TypeScript 2: custom typings for untyped npm module
  11. Exclude/overwrite npm-provided typings
  12. Difference between type[] and [type] in typescript
  13. How can I create an object based on an interface file definition in TypeScript?
  14. TypeScript typings in npm @types org packages
  15. Test for array of string type in TypeScript
  16. Can’t narrow the type of an object property even after checking it with a type guard
  17. ‘Property does not exist on type ‘never’
  18. TypeScript empty object for a typed variable
  19. ts An async function or method in ES5/ES3 requires the ‘Promise’ constructor
  20. How to declare a function that throws an error in Typescript
  21. How to use enum as index key type in typescript?
  22. Typescript: Remove entries from tuple type
  23. Typescript: change function type so that it returns new value
  24. What does a TypeScript index signature actually mean?
  25. Why does a Typescript type conditional on `T extends undefined`, with T instantiated with `boolean`, resolve T to `never`?
  26. What exactly $event object do in Angular 2?
  27. new Typescript “satisfies” operator
  28. What are the differences between the private keyword and private fields in TypeScript?
  29. Is it possible to export * as foo in typescript
  30. Narrowing a return type from a generic, discriminated union in TypeScript

Leave a Comment