What is the best way to retrieve all keys from a deeply nested object using recursion

Question

What is the best way to retrieve all keys from a deeply nested object using recursion

type NestedObject = {
 amount: number,
 error: string | null,
 data: {
  rows: [],
  messages: {
   goodNews: string | null,
   badNews: string | null
  }
 }
}

//attempting to recursively retrieve all keys 
type AllKeys<T, K extends keyof T> = 
 T extends object ?
  T extends infer O ? 
   {keys: K | AllKeys<O, keyof O> : never
 : K

type Test = AllKeys<NestedObject, keyof NestedObject>

as a result I got:

type Test = { keys: 'amount' | 'error' | 'data' | ... }

however, I aim to obtain:

type Test = { keys: 'amount' | 'error' | 'data' | 'rows' | 'messages' | 'goodNews' | 'badNews'}

typescript recursion

Answer 1

Answer №1

Seems like you're interested in something along these lines:

type RecursiveKeyof<T> = T extends object ? (
    T extends readonly any[] ? RecursiveKeyof<T[number]> : (
        keyof T | RecursiveKeyof<T[keyof T]>
    )
) : never

This function delves into object types, providing you with the keys of all nested properties and sub-properties. It excludes primitives (such as keyof string), and handles arrays differently by focusing on the keys of the array elements rather than the array itself (which would include keys like number and "push", "pop", etc).

Your AllKeys function appears to require a keys property, so it can be implemented as follows:

type AllKeys<T> = { keys: RecursiveKeyof<T> }

Let's test it out:

type Test = AllKeys<NestedObject>
// type Test = {keys: "amount" | "error" | "data" | "rows" | "messages" | "goodNews" | "badNews" }

Looks good.

Playground link to code

Answer 2

Seems like you're interested in something along these lines:

type RecursiveKeyof<T> = T extends object ? (
    T extends readonly any[] ? RecursiveKeyof<T[number]> : (
        keyof T | RecursiveKeyof<T[keyof T]>
    )
) : never

This function delves into object types, providing you with the keys of all nested properties and sub-properties. It excludes primitives (such as keyof string), and handles arrays differently by focusing on the keys of the array elements rather than the array itself (which would include keys like number and "push", "pop", etc).

Your AllKeys function appears to require a keys property, so it can be implemented as follows:

type AllKeys<T> = { keys: RecursiveKeyof<T> }

Let's test it out:

type Test = AllKeys<NestedObject>
// type Test = {keys: "amount" | "error" | "data" | "rows" | "messages" | "goodNews" | "badNews" }

Looks good.

Playground link to code

Answer 3

Answer №2

This code snippet is functioning perfectly:

interface NestedObject {
 a: number,
 b: {
  bb: string[],
  cc: string,
  dd: {
    foo: string
    bar: {
      baz: 'qqq'
    }
  }
 }
}

type AllKeys<O extends object, K = O[keyof O]> =
  keyof O
  | (
    K extends any[]
      ? never
      : K extends object
        ? AllKeys<K>
        : never
  )

type Test = AllKeys<NestedObject>

Take a look at my TypeScript playground.

Answer 4

This code snippet is functioning perfectly:

interface NestedObject {
 a: number,
 b: {
  bb: string[],
  cc: string,
  dd: {
    foo: string
    bar: {
      baz: 'qqq'
    }
  }
 }
}

type AllKeys<O extends object, K = O[keyof O]> =
  keyof O
  | (
    K extends any[]
      ? never
      : K extends object
        ? AllKeys<K>
        : never
  )

type Test = AllKeys<NestedObject>

Take a look at my TypeScript playground.

What is the best way to retrieve all keys from a deeply nested object using recursion

Answer №1

Answer №2

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