How to get a variable type in Typescript?

by

For :

abc:number|string;

Use the JavaScript operator typeof:

if (typeof abc === "number") {
    // do something
}

TypeScript understands typeof 🌹

This is called a typeguard.

More

For classes you would use instanceof e.g.

class Foo {}
class Bar {} 

// Later
if (fooOrBar instanceof Foo){
  // TypeScript now knows that `fooOrBar` is `Foo`
}

There are also other type guards e.g. in etc https://basarat.gitbook.io/typescript/type-system/typeguard

More Related Contents:

  1. When I refresh my website I get a 404. This is with Angular2 and firebase
  2. Expected 3 type arguments but got 1 but it should infer 2 types
  3. Import class in definition file (*d.ts)
  4. Typescript return type depending on parameter
  5. Mapped Types: removing optional modifier
  6. Why can I avoid excess property check in typescript just by passing a reference to an object to a function rather than the object in its literal form?
  7. TypeScript: Accept all Object keys that map to a specific type
  8. Typescript interface default values
  9. How to configure custom global interfaces (.d.ts files) for TypeScript?
  10. How to selectively assign from one Partial to another in typescript
  11. How to unwrap the type of a Promise?
  12. Experimental decorators warning in TypeScript compilation
  13. A TypeScript GUID class? [closed]
  14. How to define an opaque type in TypeScript?
  15. What is the Record type?
  16. What does “homomorphic mapped type” mean?
  17. What does “all legal JavaScript is legal TypeScript” mean?
  18. Empty interface allow any object?
  19. How to prevent unintended type compatibility in TypeScript
  20. TypeScript sorting an array
  21. “An index signature parameter type cannot be a union type.” – what should I use instead?
  22. Detailed differences between type annotation `variable: type` and type assertion `expression as type` in TypeScript
  23. Generic and typeof T in the parameters
  24. Typescript: type narrowing not working for `in` when key is stored in a variable
  25. Run factory function on import in TypeScript?
  26. How to make “handler” lookup for “dispatcher” style function be typed correctly
  27. How do I decide whether @types/* goes into `dependencies` or `devDependencies`?
  28. How to define an interface for objects with dynamic keys?
  29. Types from both keys and values of object in Typescript
  30. Modules vs. Namespaces: What is the correct way to organize a large typescript project?

Leave a Comment