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