"{}" as type in Typescript

Question

What type is a variable declared as below. In what case is it useful?

let x: {}

In the following type alias what is the meaning of {}. Is it equivalent to object or any? Why you would want to use {} as type instead of any? Does {}, in this case mean "instance" of empty object? (does make sense to me)

type MessageHandler<D, P> = (data: D, payload: P) => void
type MessageHandlerGeneric = MessageHandler<{}, any}

interface MessageHandlers {
  [index: string]: MessageHandlerGeneric
}

let handlers = MessageHandlers = {
  handler1: (data: string, payload: Pyaload),
  handler2: (data: Array<string>, payload: Payload)
}

`{}` is an object, isn't it? `any` means anything; an object, a number, a string, `undefined`, an array etc. Why do you think that `{}` is the same thing as `any`? — axiac, Jan 23 '19 at 09:11
I think you should check this answer https://stackoverflow.com/questions/18961203/any-vs-object — Whatatimetobealive, Jan 23 '19 at 09:16
As I understand it `any` also could be `undefined` or `null`. So `object` and `any` are similar to me except that the compiler doesn't perform type checks for `any`. Am I wrong? — Stanislav Stoyanov, Jan 23 '19 at 09:16
The `Object` (with capital O) mainly describes that the object has the common javascript methods like `toString` — Stanislav Stoyanov, Jan 23 '19 at 09:18
Relevant isue on TypeScript's github : https://github.com/Microsoft/TypeScript/issues/8032 — Pac0, Jan 23 '19 at 09:20
`any` has no restrictions it can be anything, but `{}` has restrictions like an object it only allows you to access to members. — Whatatimetobealive, Jan 23 '19 at 09:20

score 0 · Answer 1 · answered Jan 23 '19 at 09:33

Object is more restrictive than any.

const b: Object = {};
b.myMethod();

won't compile (where myMethod() is not declared and known method). On the other hand, the method below compiles.

const c: any = {};
c.myMethod();

So, any can be anything (including null/undefined) on the other hand, If you explicitly use Object you will only be able to use the properties that are defined on the Object class.

score 0 · Answer 2 · answered Jan 23 '19 at 09:49

As others pointed out - once variable typed as any, compiler won't warn you if you'll try to access non existing properties or assign any value.

Regarding object vs {} - object is a type that represents the non-primitive type, i.e. any thing that is not number | string | boolean | symbol.

const foo: object = 'test'; // error 
const bar: {} = 'test'; // ok

"{}" as type in Typescript

2 Answers2