Enums in Javascript with ES6

Question

I m rebuilding an old Java project in Javascript  and realized that there s no good way to do enums in JS   The best I can come up with is    const Colors         RED  Symbol  red        BLUE  Symbol  blue        GREEN  Symbol  green      Object freeze Colors     The const keeps Colors from being reassigned  and freezing it prevents mutating the keys and values  I m using Symbols so that Colors RED is not equal to 0  or anything else besides itself   Is there a problem with this formulation  Is there a better way      I know this question is a bit of a repeat  but all the previous Q As are quite old  and ES6 gives us some new capabilities      EDIT   Another solution  which deals with the serialization problem  but I believe still has realm issues   const enumValue    name    gt  Object freeze  toString       gt  name     const Colors   Object freeze       RED  enumValue  Colors RED        BLUE  enumValue  Colors BLUE        GREEN  enumValue  Colors GREEN         By using object references as the values  you get the same collision-avoidance as Symbols

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I prefer  tonethar s approach  with a little bit of enhancements and digging for the benefit of understanding better the underlyings of the ES6 Node js ecosystem  With a background in the server side of the fence  I prefer the approach of functional style around platform s primitives  this minimizes the code bloat  the slippery slope into the state s management valley of the shadow of death due to the introduction of new types and increases the readability - makes more clear the intent of the solution and the algorithm    Solution with TDD  ES6  Node js  Lodash  Jest  Babel  ESLint       utils js import   from  lodash    const enumOf       args    gt    Object freeze  Array from  Object assign args         filter   item    gt    isString item        map  item    gt  Object freeze Symbol for item       const sum    a  b    gt  a   b   export  enumOf  sum        utils js       kittens js import  enumOf  from    utils    const kittens        gt      const Kittens   enumOf null  undefined   max    joe   13  -13   tabby   new      Date     tom      return      gt  Kittens         export default kittens         kittens js        utils test js import   from  lodash   import kittens from    kittens    test  enum works as expected        gt      kittens forEach  kitten    gt           in a typed world  do your type checks        expect   isSymbol kitten            no extraction of the wrapped string here            toString is bound to the receiver s type     expect kitten toString   startsWith  Symbol     not toBe false       expect String kitten  startsWith  Symbol     not toBe false       expect   isFunction Object valueOf kitten    not toBe false        const petGift   0     Math random     2   kitten description          Symbol keyFor kitten       expect petGift startsWith  Symbol     not toBe true       console log  Unwrapped Christmas kitten pet gift    petGift    yeee                    expect     gt   kitten description    fff     toThrow                   utils test js

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As mentioned above  you could also write a makeEnum   helper function   function makeEnum arr       let obj           for  let val of arr           obj val    Symbol val             return Object freeze obj       Use it like this   const Colors   makeEnum   red   green   blue     let startColor   Colors red   console log startColor      Symbol red   if startColor    Colors red       console log  Do red things     else      console log  Do non-red things

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If you don t need pure ES6 and can use Typescript  it has a nice enum   https   www typescriptlang org docs handbook enums html

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This is my personal approach   class ColorType       static get RED              return  red              static get GREEN              return  green              static get BLUE              return  blue               Use case  const color   Color create ColorType RED

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You can check Enumify  a very good and well featured library for ES6 enums

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Whilst using Symbol as the enum value works fine for simple use cases  it can be handy to give properties to enums  This can be done by using an Object as the enum value containing the properties   For example we can give each of the Colors a name and hex value          Enum for common colors      readonly     enum   name  string  hex  string       const Colors   Object freeze     RED      name   red   hex    f00       BLUE     name   blue   hex    00f       GREEN    name   green   hex    0f0          Including properties in the enum avoids having to write switch statements  and possibly forgetting new cases to the switch statements when an enum is extended   The example also shows the enum properties and types documented with the JSDoc enum annotation   Equality works as expected with Colors RED     Colors RED being true  and Colors RED     Colors BLUE being false

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Here is an Enum factory that avoids realm issues by using a namespace and Symbol for   x000D   x000D  const Enum    n     v    gt  Object freeze v reduce  o  v    gt   o v    Symbol for    n    v     o          const COLOR   Enum  ACME Color    Blue    Red    console log COLOR Red toString     console log COLOR Red     Symbol for  ACME Color Red     x000D   x000D   x000D

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Here is my implementation of a Java enumeration in JavaScript  I also included unit tests   x000D   x000D  const main        gt      mocha setup  bdd     chai should      describe  Test Color  From Array    function         let Color   new Enum  RED    BLUE    GREEN            it  Test  Color values          gt          Color values   length should equal 3              it  Test  Color RED        gt          chai assert isNotNull Color RED              it  Test  Color BLUE        gt          chai assert isNotNull Color BLUE              it  Test  Color GREEN        gt          chai assert isNotNull Color GREEN              it  Test  Color YELLOW        gt          chai assert isUndefined Color YELLOW                 describe  Test Color  From Object    function         let Color   new Enum         RED       hex    F00           BLUE      hex    0F0           GREEN     hex    00F                it  Test  Color values          gt          Color values   length should equal 3              it  Test  Color RED        gt          let red   Color RED       chai assert isNotNull red        red getHex   should equal   F00               it  Test  Color BLUE        gt          let blue   Color BLUE       chai assert isNotNull blue        blue getHex   should equal   0F0               it  Test  Color GREEN        gt          let green   Color GREEN       chai assert isNotNull green        green getHex   should equal   00F               it  Test  Color YELLOW        gt          let yellow   Color YELLOW       chai assert isUndefined yellow                 mocha run      class Enum     constructor values        this   values          let isObject   arguments length     1     let args   isObject   Object keys values        arguments      args forEach  name  index    gt          this   createValue name  isObject   values name    null  index             Object freeze this         values         return this   values            private        createValue name  props  index        let value   new Object       value   defineGetter    name   function           return Symbol name             value   defineGetter    ordinal   function           return index            if  props          Object keys props  forEach prop   gt            value   defineGetter   prop  function               return props prop                     value   proto    get    this   capitalize prop     function               return this prop                               Object defineProperty this  name          value  Object freeze value         writable  false            this   values push this name              private        capitalize str        return str charAt 0  toUpperCase     str slice 1         main   x000D   as-console-wrapper   top  0  max-height  100   important    x000D   lt link rel  stylesheet  type  text css  href  https   cdnjs cloudflare com ajax libs mocha 2 2 5 mocha css  gt   lt script type  text javascript  src  https   cdnjs cloudflare com ajax libs mocha 2 2 5 mocha js  gt  lt  script gt   lt script type  text javascript  src  https   cdnjs cloudflare com ajax libs chai 3 2 0 chai js  gt  lt  script gt   lt  --  public enum Color     RED   F00      BLUE   0F0      GREEN   00F         private String hex    public String getHex      return this hex          private Color String hex        this hex   hex         -- gt   lt div id  mocha  gt  lt  div gt  x000D   x000D   x000D    Update Here is a more up-to-date version that satisfies MDN  The Object prototype   defineGetter   has been replaced by Object defineProperty per MDN s recomendation   This feature is deprecated in favor of defining getters using the object initializer syntax or the Object defineProperty   API  While this feature is widely implemented  it is only described in the ECMAScript specification because of legacy usage  This method should not be used since better alternatives exist    x000D   x000D  const main        gt      mocha setup  bdd     chai should      describe  Test Color  From Array    function         let Color   new Enum  RED    BLUE    GREEN        it  Test  Color values          gt          Color values   length should equal 3              it  Test  Color RED        gt          chai assert isNotNull Color RED              it  Test  Color BLUE        gt          chai assert isNotNull Color BLUE              it  Test  Color GREEN        gt          chai assert isNotNull Color GREEN              it  Test  Color YELLOW        gt          chai assert isUndefined Color YELLOW                 describe  Test Color  From Object    function         let Color   new Enum         RED      hex    F00           BLUE     hex    0F0           GREEN    hex    00F                    it  Test  Color values          gt          Color values   length should equal 3              it  Test  Color RED        gt          let red   Color RED       chai assert isNotNull red        red getHex   should equal   F00               it  Test  Color BLUE        gt          let blue   Color BLUE       chai assert isNotNull blue        blue getHex   should equal   0F0               it  Test  Color GREEN        gt          let green   Color GREEN       chai assert isNotNull green        green getHex   should equal   00F               it  Test  Color YELLOW        gt          let yellow   Color YELLOW       chai assert isUndefined yellow                 mocha run      class Enum     constructor    values        this   values           const  first     rest    values     const hasOne   rest length     0     const isArray   Array isArray first      const args   hasOne    isArray   first   Object keys first     values      args forEach  name  index    gt          this   createValue           name          index          props  hasOne  amp  amp   isArray   first name    null                      Object freeze this             public      values         return this   values            private        createValue   name  index  props          const value           Object defineProperties value  Enum   defineReservedProps         name        index              if  props          Object defineProperties value  Enum   defineAccessors props              Object defineProperty this  name          value  Object freeze value         writable  false             this   values push this name              private    Enum   defineReservedProps      name  index      gt       name        value  Symbol name       writable  false        ordinal        value  index      writable  false             private    Enum   defineAccessors    props    gt    Object entries props  reduce  acc   prop  val     gt            acc       prop           value  val        writable  false              get  Enum   capitalize prop              get       gt  function             return this prop                               private    Enum   capitalize    str    gt  str charAt 0  toUpperCase     str slice 1   main   x000D   as-console-wrapper   top  0  max-height  100   important    x000D   lt link rel  stylesheet  type  text css  href  https   cdnjs cloudflare com ajax libs mocha 2 2 5 mocha css  gt   lt script type  text javascript  src  https   cdnjs cloudflare com ajax libs mocha 2 2 5 mocha js  gt  lt  script gt   lt script type  text javascript  src  https   cdnjs cloudflare com ajax libs chai 3 2 0 chai js  gt  lt  script gt   lt  --  public enum Color     RED   F00      BLUE   0F0      GREEN   00F         private String hex    public String getHex      return this hex          private Color String hex        this hex   hex         -- gt   lt div id  mocha  gt  lt  div gt  x000D   x000D   x000D

User · Answer

You could use ES6 Map  const colors   new Map       RED    red        BLUE    blue        GREEN    green        console log colors get  RED

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Here is my approach  including some helper methods  export default class Enum        constructor name           this name   name             static get values            return Object values this              static forName name           for var enumValue of this values               if enumValue name     name                   return enumValue                                  throw new Error  Unknown value      name                    toString            return this name            -  import Enum from    enum js    export default class ColumnType extends Enum          constructor name  clazz           super name                   this associatedClass   clazz           ColumnType Integer   new ColumnType  Integer   Number   ColumnType Double   new ColumnType  Double   Number   ColumnType String   new ColumnType  String   String

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Check how TypeScript does it  Basically they do the following   const MAP        MAP MAP 1     A     1  MAP MAP 2     B     2   MAP  A      1 MAP 1     A   Use symbols  freeze object  whatever you want

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Maybe this solution       function createEnum  array      return Object freeze array      reduce  obj  item    gt          if  typeof item      string             obj item toUpperCase      Symbol item                return obj                 Example   createEnum   red    green    blue       gt   RED  Symbol red   GREEN  Symbol green   BLUE  Symbol blue

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Is there a problem with this formulation    I don t see any      Is there a better way    I d collapse the two statements into one   const Colors   Object freeze       RED    Symbol  red        BLUE   Symbol  blue        GREEN  Symbol  green         If you don t like the boilerplate  like the repeated Symbol calls  you can of course also write a helper function makeEnum that creates the same thing from a list of names

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Update 11 05 2020  Modified to include static fields and methods to closer replicate  quot true quot  enum behavior  If you re planning on updating I would recommend trying to use what I call an  quot Enum Class quot   barring any browser or runtime env limitations you can t accept   It s basically a very simple and clean class that uses private fields and limited accessors to simulate the behavior of an enum  This is something I sometimes do in C  when I want to build more functionality into an enum  I realize private class fields are still experimental at this point but it seems to work for the purposes of creating a class with immutable fields properties  Browser support is decent as well  The only  quot major quot  browsers that don t support it are Firefox  which I m sure they will soon  and IE  who cares   DISCLAIMER  I am not a developer  I just put this together to solve the limitations of nonexistent enums in JS when I was working on a personal project  Sample Class class Colors          Private Fields     static   RED   0      static   GREEN   1      static   BLUE   2          Accessors for  quot get quot  functions only  no  quot set quot  functions      static get RED     return this   RED        static get GREEN     return this   GREEN        static get BLUE     return this   BLUE       You should now be able to call your enums directly  Colors RED     0 Colors GREEN     1 Colors BLUE     2  The combination of using private fields and limited accessors means that the existing enum values are well protected  they re essentially constants now   Colors RED   10    Colors RED is still 0 Colors  RED   10    Colors RED is still 0 Colors   RED   10    Colors RED is still 0

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you can also use es6-enum package  https   www npmjs com package es6-enum   It s very easy to use  See the example below   import Enum from  es6-enum   const Colors   Enum  red    blue    green    Colors red     Symbol red

[javascript] Enums in Javascript with ES6

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