Summary - Recursive types

Write a JSON tree model with recursive types.

Summary - Recursive types

In this group you learned recursive types: self-referencing types model nested structures like linked lists and trees; DeepPartial makes nested objects deeply optional. A JSON tree model references itself in array and object forms alongside a union of primitive types.

type JsonValue =
  | string | number | boolean | null
  | JsonValue[]
  | { [k: string]: JsonValue };

Exercise Write a JSON tree model

Define a recursive union type named JsonDeger: string | number | boolean | null | JsonDeger[] | { [anahtar: string]: JsonDeger }. The veri variable should be of type JsonDeger with value { ad: "test", yas: 30 }. Print veri["ad"] with console.log.

Show example solution

type JsonDeger =
  | string
  | number
  | boolean
  | null
  | JsonDeger[]
  | { [anahtar: string]: JsonDeger };
const veri: JsonDeger = { ad: "test", yas: 30 };
console.log(veri["ad"]);

Test yourself

What should be the type of array elements in a JSON tree model?
- Only string
- JsonDeger (itself)
- any[]
- Only number
Show answer

JsonDeger (itself) — Elements of a JSON array can themselves be any JSON value; so the array type references itself as JsonDeger[].

JSON array self-reference

type JsonDeger =
  | string
  | number
  | boolean
  | null
  | ____[]
  | { [anahtar: string]: JsonDeger };

Show answer

type JsonDeger =
  | string
  | number
  | boolean
  | null
  | JsonDeger[]
  | { [anahtar: string]: JsonDeger };

Recursive types summary

JsonDeger[]

Array element is itself
{ [k: string]: JsonDeger }

Object values are itself
string | number

Primitive options
DerinPartial

Nested optional

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