Literal Types

Beginner~15 min

Literal types allow you to specify exact values a variable can have, providing precise type safety.

String Literal Types

Output

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Literal Types: Instead of allowing any string/number, limit to specific values like "north" | "south"

When to Use Literal Types

Status values: "pending" | "approved" | "rejected"
Directions: "north" | "south" | "east" | "west"
Modes: "light" | "dark" | "auto"
Fixed values: Dice rolls (1-6), HTTP methods

Literal Types vs Enums

Feature	Literal Types	Enums
Syntax	Simple union	Enum declaration
Runtime	No runtime code	Generates object
Autocomplete	✓ Yes	✓ Yes
Best for	Simple string/number sets	Complex enumerations

Common Mistakes

1. Using String Instead of Literal

// ✗ Too broad - any string allowed
function setTheme(theme: string) { }

// ✓ Precise - only specific values
function setTheme(theme: "light" | "dark") { }

2. Forgetting const Assertion

let direction = "north";  // Type: string

// ✓ Use const or as const
const direction = "north";  // Type: "north"
let dir = "north" as const;  // Type: "north"

Best Practice: Use literal types for fixed sets of values. They provide better type safety than plain strings.

Summary

Literal types specify exact values
Works with strings, numbers, booleans
Combine with unions for multiple options
Provides autocomplete and type safety

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