What are Recursive Types in TypeScript? | TypeScript Interview Questions

What You'll Learn

Recursive type patterns
Common use cases
Avoiding infinite recursion

Basic Recursive Type

code.tsTypeScript

// Tree structure
interface TreeNode {
  value: string;
  children: TreeNode[];
}

const tree: TreeNode = {
  value: "root",
  children: [
    { value: "child1", children: [] },
    { value: "child2", children: [
      { value: "grandchild", children: [] }
    ]}
  ]
};

JSON Type

code.tsTypeScript

type JSONValue =
  | string
  | number
  | boolean
  | null
  | JSONValue[]
  | { [key: string]: JSONValue };

Deeply Nested Partial

code.tsTypeScript

type DeepPartial<T> = {
  [K in keyof T]?: T[K] extends object
    ? DeepPartial<T[K]>
    : T[K];
};

interface Config {
  server: {
    host: string;
    port: number;
  };
}

type PartialConfig = DeepPartial<Config>;
// All nested properties optional

Linked List

code.tsTypeScript

interface ListNode<T> {
  value: T;
  next: ListNode<T> | null;
}

const list: ListNode<number> = {
  value: 1,
  next: {
    value: 2,
    next: {
      value: 3,
      next: null
    }
  }
};