ts-enum

Type-safe TypeScript enum utilities with perfect type inference and zero dependencies

Why Another Enum Library?

Because existing solutions are over-engineered. Popular enum libraries use wrapper objects, WeakMaps, and type assertions to work around TypeScript's limitations. This library takes a different approach: work with TypeScript's type system, not against it.

import { Enum } from '@castral/ts-enum';

enum Status { Idle = 0, Running = 1, Complete = 2 }

// ✅ Perfect type inference - no casts needed
const keys = Enum.keys(Status);      // ("Idle" | "Running" | "Complete")[]
const values = Enum.values(Status);  // Status[] (= (0 | 1 | 2)[])

// ✅ Literal types preserved through type guards
const value = 1;
if (Enum.isValue(Status, value)) {
  // value is narrowed to Status.Running
}

// ✅ TypeScript proves unreachable code
const invalid = 99;
if (Enum.isValue(Status, invalid)) {
  // Type: never - TypeScript knows this will never execute!
}

Features

• 🎯 Perfect Type Inference - Literal union types, not generic string[] or number[]
• 🔍 Exact Member Narrowing - Type guards narrow to specific enum members, not just unions
• ⚡ Zero Dependencies - No external packages, just pure TypeScript
• 📦 Tiny Bundle - ~1KB minified, tree-shakeable
• 🛡️ Type-Safe - Works with single Enums as well as unions of Enums, ie: typeof FirstEnum | typeof SecondEnum
• ✅ Compile-Time Proof - TypeScript mathematically proves correctness
• 🔧 Works Everywhere - Numeric enums, string enums, and mixed enums

Installation

npm install @castral/ts-enum

yarn add @castral/ts-enum

pnpm add @castral/ts-enum

Quick Start

import { Enum } from '@castral/ts-enum';

enum Priority {
  Low = 1,
  Medium = 2,
  High = 3
}

// Get enum keys with exact literal types
const keys = Enum.keys(Priority);
// Type: ("Low" | "Medium" | "High")[]
// Value: ["Low", "Medium", "High"]

// Get enum values with exact literal types
const values = Enum.values(Priority);
// Type: Priority[] (= (1 | 2 | 3)[])
// Value: [1, 2, 3]

// Type-safe validation
function handlePriority(value: unknown) {
  if (Enum.isValue(Priority, value)) {
    // value is narrowed to Priority
    console.log('Valid priority:', value);
  }
}

API Reference

Enum.keys<E>(enum)

Returns an array of enum keys with exact literal types.

enum Status { Idle = 0, Running = 1 }

const keys = Enum.keys(Status);
// Type: ("Idle" | "Running")[]
// Not: string[] ❌

Enum.values<E>(enum)

Returns an array of enum values with exact literal types.

enum Status { Idle = 0, Running = 1 }

const values = Enum.values(Status);
// Type: Status[] (= (0 | 1)[])
// Not: (string | number)[] ❌

Enum.entries<E>(enum)

Returns an array of [key, value] tuples with exact types.

enum Status { Idle = 0, Running = 1 }

const entries = Enum.entries(Status);
// Type: [("Idle" | "Running"), Status][]
// Value: [["Idle", 0], ["Running", 1]]

Enum.isKey<E>(enum, key)

Type guard that narrows to exact enum keys.

enum Status { Idle = 0, Running = 1 }

function parse(key: unknown) {
  if (Enum.isKey(Status, key)) {
    const val = Status[key];
    console.log(`Status is ${key}: ${val}`);
  }
}

// Must exactly match enum key
const invalid = 'idle';
if (Enum.isKey(Status, invalid)) {
  // Type: never - this will never execute!
}

Enum.isValue<E>(enum, value)

Type guard that narrows to exact enum values.

enum Status { Idle = 0, Running = 1 }

function process(value: unknown) {
  if (Enum.isValue(Status, value)) {
    // value is narrowed to Status
    switch (value) {
      case Status.Idle:    // ✅ Type-safe
      case Status.Running: // ✅ Type-safe
    }
  }
}

const invalid = 99;
if (Enum.isValue(Status, invalid)) {
  // Type: never - this will never execute!
}

Enum.createIsKeyGuard<E>(enum)

Creates a reusable key type guard with cached keys (O(1) lookup).

enum Status { Idle = 0, Running = 1 }

const isStatus = Enum.createIsKeyGuard(Status);

// Use in hot paths for better performance
if (isStatus(key)) {
  // key is narrowed to Status
}

Enum.createIsValueGuard<E>(enum)

Creates a reusable value type guard with cached values (O(1) lookup).

enum Status { Idle = 0, Running = 1 }

const isStatus = Enum.createIsValueGuard(Status);

// Use in hot paths for better performance
if (isStatus(value)) {
  // value is narrowed to Status
}

Enum.map<E, T>(enum, fn)

Transform enum entries with type-safe callback.

enum Priority { Low = 1, Medium = 2, High = 3 }

const options = Enum.map(Priority, (key, value) => ({
  label: key,        // Type: "Low" | "Medium" | "High"
  value: value,      // Type: 1 | 2 | 3
  priority: value
}));

Enum.keyOf<E>(enum, value)

Reverse lookup: get key from value.

enum Status { Idle = 0, Running = 1 }

const key = Enum.keyOf(Status, 1);
// Type: ("Idle" | "Running") | undefined
// Value: "Running"

Enum.keyOfStrict<E>(enum, value)

Strict reverse lookup: throws if value not found.

enum Status { Idle = 0, Running = 1 }

const key = Enum.keyOfStrict(Status, 1);
// Type: "Idle" | "Running"
// Throws if value is not 0 or 1

Enum.keyOfValueToString<E>(enum, value)

Convert enum value to string key.

enum Status { Idle = 0, Running = 1 }

const str = Enum.keyOfValueToString(Status, Status.Idle);
// Type: string | undefined
// Value: "Idle"

Enum.valueOfKey<E>(enum, Key<E>)

enum Status { Idle = 0, Running = 1 }

const value = Enum.valueOfKey(Status, Enum.keys(Status)[1] ?? 'Idle');
// Type: Status
// Value: 1

Enum.get<E>(enum, key: unknown)

enum Status { Idle = 0, Running = 1 }

const currentStatus: string | undefined = 'Running';

const value = Enum.get(Status, currentStatus);
// Type: Status | undefined
// Value: 1

Enum.valueOfKeyFromString<E>(enum, string)

Parse string to enum value (case-insensitive).

enum Status { Idle = 0, Running = 1 }

const value = Enum.valueFromKeyString(Status, 'idle');
// Type: Status | undefined
// Value: 0

Advanced Type Inference

Exact Member Narrowing

Unlike other libraries, ts-enum narrows to exact enum members, not just the union type.

enum Color { Red = 'red', Blue = 'blue' }

const literal = 'red';

if (Enum.isValue(Color, literal)) {
  // Other libraries: literal has type Color (= Color.Red | Color.Blue)
  // This library:    literal has type Color.Red
  
  const exact: Color.Red = literal;  // ✅ Works!
}

Literal Type Preservation

TypeScript can prove compile-time value mappings.

enum Status { Idle = 0, Running = 1 }

const value = 0;  // Literal type: 0

if (Enum.isValue(Status, value)) {
  // value is proven to be Status.Idle at compile time
  const idle: Status.Idle = value;  // ✅ No cast needed
}

const invalid = 99;  // Literal type: 99

if (Enum.isValue(Status, invalid)) {
  const x = invalid;  // Type: never
  // This code is unreachable!
}

Type Helpers

Extract types from enums at compile time.

enum Status { Idle = 0, Running = 1, Complete = 2 }

type StatusKey = Enum.Key<typeof Status>;
// = "Idle" | "Running" | "Complete"

type StatusValue = Enum.Value<typeof Status>;
// = Status.Idle | Status.Running | Status.Complete
// = 0 | 1 | 2

vs. Native Object Methods

enum Status { Idle = 0, Running = 1 }

// ❌ Object.keys() - loses type information
Object.keys(Status)     // string[] (includes "0", "1")
Object.values(Status)   // (string | number)[]

// ✅ Enum utilities - preserves exact types
Enum.keys(Status)       // ("Idle" | "Running")[]
Enum.values(Status)     // Status[] (= (0 | 1)[])

Use Cases

Compile-Time Configuration

enum AgentPaths {
  dashboard = 'Agent Dashboard',
}

enum StreamPaths {
  overview = 'Stream Overview',
}

const Outlets = {
  agent: AgentPaths,
  stream: StreamPaths,
} as const;

interface Route<T extends keyof typeof Outlets> {
  component: any;
  outlet: T;
  path: Enum.Key<Enum.EnumLike<(typeof Outlets)[T]>>;
}

const ROUTES: (Route<'agent'> | Route<'stream'>)[] = [
  {
    component: AgentDashboard,
    outlet: 'agent',
    // Type is typeof AgentPaths
    path: 'dashboard', // Can't be 'overview'
  },
  {
    component: StreamOverview,
    outlet: 'stream',
    // Type is typeof StreamPaths
    path: 'overview', // Can't be 'dashboard'
  },
] as const;

const currentPath = 'dashboard';
Object.keys(Outlets).forEach((outlet) => {
  // Type is: typeof AgentPaths | typeof StreamPaths
  const titleEnum = Outlets[outlet as keyof typeof Outlets]; 
  const pageTitle = Enum.get(titleEnum, currentPath) ?? 'Unknown Page';
})

Form Select Options

enum Priority { Low = 1, Medium = 2, High = 3 }

const options = Enum.map(Priority, (key, value) => ({
  label: key,
  value: value,
  color: value === Priority.High ? 'red' : 'gray'
}));

// Type: { label: "Low" | "Medium" | "High", value: 1 | 2 | 3, color: string }[]

API Validation

enum HttpStatus {
  OK = 200,
  BadRequest = 400,
  Unauthorized = 401,
  NotFound = 404
}

const isHttpStatus = Enum.createIsValueGuard(HttpStatus);

function handleResponse(status: number) {
  if (isHttpStatus(status)) {
    // status is narrowed to HttpStatus
    console.log(`Status: ${Enum.keyOf(HttpStatus, status)}`);
  } else {
    console.error('Unknown status code');
  }
}

Exhaustive Switching

enum Action { Create = 'create', Update = 'update', Delete = 'delete' }

function handle(action: Action) {
  switch (action) {
    case Action.Create:
      return 'creating';
    case Action.Update:
      return 'updating';
    case Action.Delete:
      return 'deleting';
    // TypeScript enforces exhaustiveness - no default needed!
  }
}

Runtime Validation

enum Role { Admin = 'admin', User = 'user', Guest = 'guest' }

function parseRole(input: unknown): Role {
  if (Enum.isValue(Role, input)) {
    return input;  // Type: Role
  }
  throw new Error(`Invalid role: ${input}`);
}

Works With All Enum Types

Numeric Enums

enum Status { Idle = 0, Running = 1, Complete = 2 }

Enum.keys(Status)    // ("Idle" | "Running" | "Complete")[]
Enum.values(Status)  // (0 | 1 | 2)[]

String Enums

enum Color { Red = 'red', Blue = 'blue', Green = 'green' }

Enum.keys(Color)    // ("Red" | "Blue" | "Green")[]
Enum.values(Color)  // ("red" | "blue" | "green")[]

Mixed Enums

enum Mixed { A = 1, B = 2, C = 'c', D = 'd' }

Enum.keys(Mixed)    // ("A" | "B" | "C" | "D")[]
Enum.values(Mixed)  // (1 | 2 | "c" | "d")[]

TypeScript Configuration

For best results, use strict mode:

{
  "compilerOptions": {
    "strict": true,
    "noUncheckedIndexedAccess": true
  }
}

Why This Works

This library leverages TypeScript's type system correctly:

1. No wrapper objects - Direct enum access preserves type information
2. Proper type predicates - v is E[keyof E & string] enables narrowing
3. Literal type preservation - TypeScript can prove exact value mappings
4. Control flow analysis - Type guards work with TypeScript's narrowing

Other libraries fight the type system with runtime structures (WeakMaps, wrappers) and type assertions. This library works with TypeScript to let it prove correctness.

Contributing

Contributions welcome! Please open an issue or PR.

License

MIT © Cas Argilla

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Note: This library does not work with const enum because const enums are compile-time only and have no runtime representation. Use regular enums instead.