Functions

InstanceType

What a constructor produces when you call it with `new`.

What it is

The class version of `ReturnType`, and the reason it exists separately is that a class name means two things: the constructor value and the instance type. `typeof Foo` is the constructor; `Foo` is already the instance. `InstanceType` matters when you only have the constructor — passed as an argument, stored in a registry, produced by a factory.

Examples

```
InstanceType<typeof Session>
```
→Session
```
ConstructorParameters<typeof Session>
```
→[]
```
InstanceType<typeof Session>['id']
```
→string
Once you have the instance type, everything else — `keyof`, indexed access, mapped types — applies as normal.

Each resolved type above was printed by TypeScript 5.9.3, not written by hand.

What it does not do

It does not accept the class name directly. `InstanceType<Session>` is an error, because `Session` is already the instance — you want `typeof Session`.
It does not include static members. Those live on the constructor, which is the thing you passed in, not the thing you got out.

Takeaway

A class name is two types wearing one word. `typeof C` is the constructor, `C` is the instance, and almost every confusing class-generic error is those two swapped.