Day 14: Literal Types and Enums

Exact Values

Welcome to Day 14! Sometimes string or number is too broad. sometimes we want specific strings or numbers.

Literal Types

You can use a specific string or number as a type properly.

let direction: "left" | "right" | "up" | "down";
direction = "left"; // OK
// direction = "diagonal"; // Error

This is incredibly powerful when paired with Union Types.

Enums

Enums (Enumerations) allow you to define a set of named constants.

Numeric Enums

By default, they are numbers starting at 0.

enum Direction {
  Up,     // 0
  Down,   // 1
  Left,   // 2
  Right,  // 3
}

move(Direction.Up);

String Enums

You can initialize them with strings for better debugging.

enum Role {
  User = "USER",
  Admin = "ADMIN",
}

Literals vs Enums

• Literal Types: Lightweight, simpler, no runtime code generated. Great for simple unions.
• Enums: More rigid, generate actual JavaScript code (an object). Good if you need to iterate over the values or use them as actual values at runtime.

Modern TS Advice: Lean towards Literal Types or const objects (as const) unless you specifically need Enum features.

Challenge for Today

1. Create a function move(direction: "Up" | "Down" | "Left" | "Right").
2. Try to call it with “North”.
3. Create an Enum Status with Pending, InProgress, Done.
4. Create a function updateStatus(s: Status).

See you on Day 15 for the big one: Generics!