Enums

Syntax

enum Name { Member1, Member2 }

Examples

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

enum Status {
  Pending = "PENDING",
  Active = "ACTIVE",
  Completed = "COMPLETED"
}

function move(direction: Direction) {
  console.log(Direction[direction]); // reverse lookup: "Up", "Down", etc for numeric enums
}

move(Direction.Up);
console.log(Status.Active); // "ACTIVE"

const enum Size {
  Small,
  Medium,
  Large
}

let mySize = Size.Medium;
// Compiles down to: let mySize = 1;
// No Size object exists at runtime at all - completely inlined

Best practices

• Consider a literal type union ("small" | "medium" | "large") instead of an enum for simple cases - it requires no import and integrates more naturally with plain JS
• Use string enums over numeric enums when the value might be logged, serialized, or debugged, since string values are self-explanatory
• Use const enum only when you specifically want zero runtime footprint and do not need reverse lookups - be aware it has some restrictions in certain build tools
• Avoid mixing numeric and string values within the same enum, as it can produce confusing reverse-lookup behavior

At a glance

Purpose

Static types for JavaScript

File extension

.ts · .tsx

Runs in

Compiled to JavaScript

Usually used with

JavaScript and its ecosystem

Specifications & further reading

• TypeScript Handbook

Related TypeScript documentation