NestedKeyOf

NestedKeyOf.ts

type NestedKeyOf<ObjectType extends object> = 
{[Key in keyof ObjectType & (string | number)]: ObjectType[Key] extends object 
? `${Key}` | `${Key}.${NestedKeyOf<ObjectType[Key]>}`
: `${Key}`
}[keyof ObjectType & (string | number)];

Extremely useful type 🚀

Here's a quick way to prevent it from iterating through array structures:

type NestedKeyOf<ObjectType extends object> = 
{[Key in keyof ObjectType & (string | number)]: ObjectType[Key] extends object ? 
    ObjectType[Key] extends { pop: any; push: any } ? `${Key}` : `${Key}` | `${Key}.${NestedKeyOf<ObjectType[Key]>}`
: `${Key}`
}[keyof ObjectType & (string | number)];

Any idea on how to support optional types here?
Let's imagine I do have to following object:
{
name: string,
address?: {
city: string
}
}

In this case this solution doesn't work. Any solution for this?

@JWThewes one could extract the "object" from the T | undefined union with the following intersection T & {}, which matches any non-null object.

So, something like this should do the trick, not sure if it has extra side-effects, but it shouldn't.

type NestedKeyOf<ObjectType extends object> = 
{[Key in keyof ObjectType & (string | number)]: ObjectType[Key] & {} extends object
? `${Key}` | `${Key}.${NestedKeyOf<ObjectType[Key] & {}>}`
: `${Key}`
}[keyof ObjectType & (string | number)];