Union & Litteral Types

Union types let a value be one of several possibilities, while literal types restrict values to exact constants:

type Status = 'idle' | 'loading' | 'success' | 'error';
type Id = string | number;
let status: Status = 'loading'; // ✅ OK
let status: Status = 'pending'; // ❌ Error

TypeScript performs control-flow narrowing: inside branches guarded by typeof, equality checks, or switch, the compiler refines a union to a specific member, giving you type safety and better autocompletion.

In this category, you'll:

Create unions of primitives (string | number)
Use literal types for statuses, directions, and modes
Narrow unions with typeof, equality checks, and switch
Work with discriminated unions (tagged with fields like kind or type)

This category focuses on practical everyday patterns: clear narrowing and small, well-defined state sets.

Status Literals

Format ID Union

Parse Boolish

Move by Direction

Shape Area