Enum

A simple and flexible Enum class for JavaScript / TypeScript.

@manoruchan/enum is an Enum class implementation

that maintains your values as constant variable after its instantiation

and supports extension with your own methods.

Why use this instead of the native enum?

Because @manoruchan/enum offers custom method definition and supports dynamic enums,

just like Java's Enum class but simpler and more flexible for JavaScript / TypeScript.

Furthermore, @manoruchan/enum now supports full type inference and autocomplete via the new Enum.create() static factory method.

Installation

npm install @manoruchan/enum

Usage

Basic Usage

import { Enum } from "@manoruchan/enum";

const Color = Enum.create([
    "RED",
    "GREEN",
    "BLUE"
] as const);

console.log(Color.RED);            // 0
console.log(Color.valueOf("RED")); // 0
console.log(Color.get(0));         // 'RED'
console.log(Color.values());       // [ 0, 1, 2 ]
console.log(Color.names());        // [ 'RED', 'GREEN', 'BLUE' ]
console.log(Color.toArray());      // [ [ 'RED', 0 ], [ 'GREEN', 1 ], [ 'BLUE', 2 ] ]

With Custom Values

import { Enum } from "@manoruchan/enum";

const Fruits = Enum.create({
    APPLE: "red",
    ORANGE: "orange",
    BANANA: "yellow"
});

console.log(Fruits.APPLE);             // red
console.log(Fruits.valueOf("ORANGE")); // 'orange'
console.log(Fruits.get("yellow"));     // 'BANANA'
console.log(Fruits.values());          // [ 'red', 'orange', 'yellow' ]

Enum With Operations

import { Enum, EnumValue } from "@manoruchan/enum";

class Week extends Enum {
    public isWeekend(day: EnumValue): boolean {
        return day === this.SAT || day === this.SUN;
    }
}

const days = ["MON", "TUE", "WED", "THU", "FRI", "SAT", "SUN"] as const;
const week = Week.create(days);

console.log(week.isWeekend(week.SUN)); // true
console.log(week.isWeekend(week.TUE)); // false

class HttpCode extends Enum<Record<string, number>> {
    public isError(value: number): boolean {
        return value >= 400;
    }

    public isClientError(value: number): boolean {
        return this.BAD_REQUEST <= value && value < this.INTERNAL_SERVER_ERROR;
    }
}

const codes = {
    OK: 200,
    BAD_REQUEST: 400,
    NOT_FOUND: 404,
    INTERNAL_SERVER_ERROR: 500,
} as const;

const http = HttpCode.create(codes);

console.log(http.isClientError(http.NOT_FOUND)); // true
console.log(http.isError(http.OK)); // false

Important Note on Autocomplete

To ensure proper type inference for array input to constructor, the argument must be annotated with as const.

Example (Array Input with Autocomplete)

// `as const` is required here
const Status= Enum.create(["ACTIVE", "INACTIVE"] as const);

console.log(Status.ACTIVE); // 0
// without `as const`, autocomplete is not available for Status.ACTIVE

Example (Object Input with Autocomplete)

// as const is not required here, but recommended.
const Fruits = Enum.create({
    APPLE: "red",
    ORANGE: "orange",
    BANANA: "yellow"
});
// } as const);

console.log(Fruits.APPLE); // red

EnumValue

type EnumValue = string | number | boolean;

EnumValue accepts primitive types.

API

static create(v: readonly string[] | Record<string, EnumValue>): Enum Creates a type-safe Enum instance. The return type provides full autocomplete based on the input v.

get(value: EnumValue): string | undefined Obtains the name associated with the enum value.

valueOf(name: string): EnumValue | undefined Obtains the enum value from its name.

values(): EnumValue[] Returns the array of enum values.

names(): string[] Returns the array of the name of enum values.

toArray(): [string, EnumValue][] Returns the entries of names and values.

LICENSE

MIT