Enums

Functional enum implementation for JS based on @rbuckton's enum proposal.

Install

npm install --save fun-enums

Usage

const { enums } = require('fun-enums');

// Default initialization
const weekdays = enums()("monday", "tuesday", "wednesday", "thursday", "friday");

weekdays.monday; // 0
weekdays.friday; // 4

Enums are frozen and should not be mutated after initializing. To avoid allowing mutation custom enum values should not be objects of depths greater than 1.

Initializers

fun-enums is built around "initializers" which allow you to change the behavior of how the enum is created. The default initalizer is number which sets the first enum value to 0 and increments each following by 1. fun-enums also exposes a string initializer which sets the value equal to the given enum name.

const { enums, string, number } = require('fun-enums');
// Provide other initializers from the package like string
let colors = enums(string)('red', 'green', 'blue')
colors.red; // 'red'

colors = enums(number)('red', 'green', 'blue'); // number does not need to be specified as it is the default behavior
colors.red // 0

Custom initializers

You can also provide your own custom initializers by passing in an initialization function to enums.

const { enums } = require('fun-enums');

function capitalize(en, _prevValue) {
  return en.charAt(0).toUpperCase() + en.slice(1);
}

const colors = enums(capitalize)('red', 'green', 'blue');
colors.red; // 'Red'

Your initializer will be passed these arguments:

arg	type	description
enum	string	the string value passed to the enum to be used as the key
prevValue	any	the value of the previous enum initialized. Used to increment enum values

Override syntax

In some cases you want a bit more control over the exact values on your enum. You can override the normal behavior of any given initializer by passing in an object rather than an array.

const { enums } = require('fun-enums');

const colors = enums()({ red: '#f44242', green: '#27c65a', blue: '#003bff' });
colors.red; // '#f44242'

This allows you to give values when running a function may not be the best method for defining the enum. You can also "opt-in" to the initializer whenever you want even when overriding by giving a key undefined.

const { enums, string } = require('fun-enums');

const names = enums(string)({ john: 'johnny', sarah: undefined, tim: 'timothy' });
names.sarah; // 'sarah'
names.tim; // 'timothy'

Objects and Arrays are invalid types for enum values and will be overwritten by default behavior when found.

Enums API

fun-enums follows a similar API as defined by @rbuckton's enums impementing keys, values, entries, has, hasValue, and getName on each enum object.

.keys()

const { enums } = require('fun-enums');

const colors = enums()('red', 'green', 'blue');
colors.keys(); // ['red', 'green', 'blue']

.values()

const { enums } = require('fun-enums');

const colors = enums()('red', 'green', 'blue');
colors.values(); // [0, 1, 2]

.entries()

const { enums } = require('fun-enums');

const colors = enums()('red', 'green', 'blue');
colors.entries(); // [['red', 0], ['green', 1], ['blue', 2]]

.has()

const { enums } = require('fun-enums');

const colors = enums()('red', 'green', 'blue');
colors.has('red'); // true
colors.has('purple'); // false

.hasValue()

const { enums } = require('fun-enums');

const colors = enums()('red', 'green', 'blue');
colors.hasValue(0); // true
colors.hasValue('red'); // false

.getName()

const { enums } = require('fun-enums');

const colors = enums()('red', 'green', 'blue');
colors.getName(0); // 'red'
colors.getName(99); // undefined