The Differences Between 'Object', '{}', and 'object' in TypeScript

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In TypeScript, when we want to define an object type, there are several concise options such as 'Object', '{}', and 'object'. What are the differences between them?

Object (uppercased)

Object (uppercased) describes properties common to all JavaScipt objects. It is defined in the lib.es5.d.ts file that comes with the TypeScript library.

As you can see, it includes some common properties like toString(), valueOf(), and so on.

Because it emphasizes only those properties that are common to JavaScript objects. So you can assign boxable objects like string, boolean, number, bigint, symbol to it, but not the other way around.

{}

{} describes an object that has no members of its own, which means TypeScript will complain if you try to access its property members:

From the code example above, we can see that {} and Object (uppercased) have the same features. That is, it can only access those properties that are common (even if the JavaScript code logic is correct), all boxable objects can be assigned to it, etc.

This is because the {} type can access those common properties through the prototype chain, and it also has no own properties. So it behaves the same as the Object (uppercased) type. But they represent different concepts.

object (lowercased)

object (lowercased) means any non-primitive type, which is expressed in code like this:

type PrimitiveType =
  | undefined
  | null
  | string
  | number
  | boolean
  | bigint
  | symbol;

type NonPrimitiveType = object;

This means that all primitive types are not assignable to it, and vice versa.

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Comments

[leob]

Great post, this is the kind of content that we want to see on dev.to, don't we? :-)

I was totally unaware of "lowercase object" (but I did hear about "Record") - super confusing, as is often the case with Javascript and TypeScript, for historical reasons of how it "came to be" ...

I honestly have no idea why they added "lowercase object", and would never recommend using it in place of "Record", but anyway, nice to know about it.

[Igor Rubinovich]

In "This means that all non-primitive types are not assignable to it, and vice versa." you probably meant "assignable" without the "not"

[Hans]

They probably meant “all primitive types”, since that’s what’s demonstrated in the code block.

[Zachary Lee]

Thanks for your tip, I fixed it.

[tonny_x_bit]

Your teaching is very good. I became know about object.

[bakare damilola]

Great content, I'll definitely be referencing this a lot till it's stuck in my brain.

[Mostafa]

It's not recommend to use type object, Object and {}
Btw Object it's not typescript specifications, and object a constructive type rarely can be used, maybe if you're writing a library declaration.

[Dipak Ahirav]

Nice very useful!

[diego fernandez]

Thanks You, easy to understand.

[blackr1234]

So the lowercase one is more strict, weird.

[Sy Hung Doan]

Informative!