Const Enums and Alternatives

Const enum inlining, package-boundary hazards, and string literal unions as the usual alternative.

const enum usually inlines values at use sites and emits no runtime object. That optimization is fragile across package boundaries.

Inlining is useful only when the whole project is compiled consistently.

const enum Axis {
  X = "x",
  Y = "y",
  Z = "z",
}
 
function rotate(axis: Axis, degrees: number): string {
  return `rotate ${degrees} on ${axis}`;
}
 
console.log(rotate(Axis.X, 90));

String literal unions often give the same safety with no emit, no import, and natural JSON values.

type Role = "admin" | "member" | "guest";
 
function greet(role: Role): string {
  return role === "admin" ? "Welcome, admin." : `Hello, ${role}.`;
}
 
const payload = { userId: "u-1", role: "admin" as Role };
console.log(JSON.stringify(payload));

In production

Use const enum only inside a single TypeScript package compiled by one toolchain. Avoid ambient const enums in published declarations, and prefer string literal unions for external contracts.

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