TypeScript-All-In-One(A.R)

Recursive Types

A Recursive Type is a type that can refer to itself. This is useful for defining data structures that have a hierarchical or recursive structure (potentially infinite nesting), such as linked lists, trees, and graphs.

type ListNode<T> = {
    data: T;
    next: ListNode<T> | undefined;
};

Recursive Conditional Types

It is possible to define complex type relationships using logic and recursion in TypeScript. Let’s break it down in simple terms:

Conditional Types: allows you to define types based on boolean conditions:

type CheckNumber<T> = T extends number ? 'Number' : 'Not a number';
type A = CheckNumber<123>; // 'Number'
type B = CheckNumber<'abc'>; // 'Not a number'

Recursion: means a type definition that refers to itself within its own definition:

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

const data: Json = {
    prop1: true,
    prop2: 'prop2',
    prop3: {
        prop4: [],
    },
};

Recursive Conditional Types combine both conditional logic and recursion. It means that a type definition can depend on itself through conditional logic, creating complex and flexible type relationships.

type Flatten<T> = T extends Array<infer U> ? Flatten<U> : T;

type NestedArray = [1, [2, [3, 4], 5], 6];
type FlattenedArray = Flatten<NestedArray>; // 2 | 3 | 4 | 5 | 1 | 6