TypeScript enum to object array

Question

I have an enum defined this way   export enum GoalProgressMeasurements       Percentage   1      Numeric Target   2      Completed Tasks   3      Average Milestone Progress   4      Not Measured   5     However  I d like it to be represented as an object array list from our API like below     id  1  name   Percentage       id  2  name   Numeric Target      id  3  name   Completed Tasks      id  4  name   Average Milestone Progress      id  5  name   Not Measured      Is there are easy and native way to do this or do I have to build a function that casts the enum to both an int and a string  and build the objects into an array

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First we get an array of keys for this enum  Then  using the map    function  we convert the data to the desired format  id is obtained from the key  name is obtained from enum by the same key   const converted   Object keys GoalProgressMeasurements  map key   gt            return               id  GoalProgressMeasurements key               name  key

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I m surprised in a TypeScript thread no one gave valid TypeScript function with typing supported  Here s variation of  user8363 solution  const isStringNumber    value  string    gt  isNaN Number value       false   function enumToArray lt T extends    gt  givenEnum  T      return  Object keys givenEnum  filter isStringNumber  as  keyof T     map       key    gt  givenEnum key

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I didn t like any of the above answers because none of them correctly handle the mixture of strings numbers that can be values in TypeScript enums  The following function follows the semantics of TypeScript enums to give a proper Map of keys to values  From there  getting an array of objects or just the keys or just the values is trivial         Converts the given enum to a map of the keys to the values      param enumeration The enum to convert to a map      function enumToMap enumeration  any   Map lt string  string   number gt      const map   new Map lt string  string   number gt       for  let key in enumeration            TypeScript does not allow enum keys to be numeric       if   isNaN Number key    continue         const val   enumeration key  as string   number           TypeScript does not allow enum value to be null or undefined       if  val     undefined  amp  amp  val     null            map set key  val          return map     Example Usage  enum Dog       Rover   1      Lassie    quot Collie quot       Fido   3      Cody    quot Mutt quot      let map   enumToMap Dog     Map of keys to values  let objs   Array from map entries    map m   gt    id  m 1   name  m 0        Objects as asked for in OP let entries   Array from map entries       Array of each entry let keys   Array from map keys       An array of keys let values   Array from map values       An array of values  I ll also point out that the OP is thinking of enums backwards  The  quot key quot  in the enum is technically on the left hand side and the value is on the right hand side  TypeScript allows you to repeat the values on the RHS as much as you d like

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x000D   x000D  enum GoalProgressMeasurements   x000D      Percentage   1  x000D      Numeric Target   2  x000D      Completed Tasks   3  x000D      Average Milestone Progress   4  x000D      Not Measured   5 x000D    x000D       x000D  const array      x000D       x000D  for  const  key  value  of Object entries GoalProgressMeasurements     x000D      if   Number isNaN Number key      x000D          continue  x000D        x000D   x000D      array push   id  value  name  key replace              x000D    x000D   x000D  console log array   x000D   x000D   x000D

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Enums are real objects that exist at runtime  So you are able to reverse the mapping doing something like this   let value   GoalProgressMeasurements Not Measured  console log GoalProgressMeasurements value         gt  Not Measured   Based on that you can use the following code   export enum GoalProgressMeasurements       Percentage   1      Numeric Target   2      Completed Tasks   3      Average Milestone Progress   4      Not Measured   5    let map   id  number  name  string           for var n in GoalProgressMeasurements        if  typeof GoalProgressMeasurements n       number             map push  id   lt any gt GoalProgressMeasurements n   name  n             console log map     Reference  https   www typescriptlang org docs handbook enums html

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Since enums with Strings values differ from the ones that have number values it is better to filter nonNumbers from  user8363 solution  Here is how you can get values from enum either strings  numbers of mixed   x000D   x000D        Helper     export const StringIsNotNumber   value   gt  isNaN Number value       true              Turn enum into array     export function enumToArray enumme          return Object keys enumme          filter StringIsNotNumber          map key   gt  enumme key          x000D   x000D   x000D

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class EnumHelpers        static getNamesAndValues lt T extends number gt  e  any            return EnumHelpers getNames e  map n   gt     name  n  value  e n  as T                 static getNames e  any            return EnumHelpers getObjValues e  filter v   gt  typeof v      string   as string               static getValues lt T extends number gt  e  any            return EnumHelpers getObjValues e  filter v   gt  typeof v      number   as T               static getSelectList lt T extends number  U gt  e  any  stringConverter   arg  U    gt  string            const selectList   new Map lt T  string gt             this getValues e  forEach val   gt  selectList set val as T  stringConverter val as unknown as U             return selectList             static getSelectListAsArray lt T extends number  U gt  e  any  stringConverter   arg  U    gt  string            return Array from this getSelectList e  stringConverter   value   gt     value  value 0  as T  presentation  value 1                  private static getObjValues e  any    number   string              return Object keys e  map k   gt  e k

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There is a simple solution  So when you run Object keys Enum  that gonna give you a Array of Values and Keys  in first slice Values and in the second one keys  so why we don t just return the second slice  this code below works for me  enum Enum      ONE     TWO     THREE     FOUR     FIVE     SIX     SEVEN   const keys   Object keys Enum    console log keys slice keys length   2

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Here s the simple function with correct typing I use        Helper to produce an array of enum values      param enumeration Enumeration object      export function enumToArray lt T  G extends keyof T   keyof T gt  enumeration  T   T G           tslint disable  comment-format       enum Colors          WHITE   0         BLACK   1              Object values Colors  will produce   WHITE    BLACK   0  1        So  simply slice the second half   const enumValues   Object values enumeration     return enumValues slice enumValues length   2  enumValues length  as T G        Usage example  enum Colors     Red   1    Blue   2    enumToArray Colors

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If you are using ES8 For this case only it will work perfectly fine  It will give you value array of the given enum  enum Colors     WHITE   0    BLACK   1    BLUE   3    const colorValueArray   Object values Colors        WHITE    BLACK    BLUE   0  1  3    You will get colorValueArray like this    WHITE    BLACK    BLUE   0  1  3    All the keys will be in first half of the array and all the values in second half  Even this kind of enum will work fine enum Operation       READ      WRITE      EXECUTE    But this solution will not work for Heterogeneous enums like this enum BooleanLikeHeterogeneousEnum     No   0    Yes    quot YES quot

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I use  Object entries GoalProgressMeasurement  filter e   gt   isNaN e 0 as any   map e   gt     name  e 1   id  e 0         A simple 1 line that does the job   It does the job in 3 simple steps  - Loads the combination of keys  amp  values using Object entries   - Filters out the non numbers  since typescript generates the values for reverse lookup    - Then we map it to the array object we like

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A tricky bit is that TypeScript will  double  map the enum in the emitted object  so it can be accessed both by key and value   enum MyEnum       Part1   0      Part2   1     will be emitted as       Part1  0     Part2  1     0   Part1      1   Part2      So you should filter the object first before mapping  So  Diullei  s solution has the right answer  Here is my implementation      Helper const StringIsNumber   value   gt  isNaN Number value       false      Turn enum into array function ToArray enumme        return Object keys enumme           filter StringIsNumber           map key   gt  enumme key        Use it like this   export enum GoalProgressMeasurements       Percentage      Numeric Target      Completed Tasks      Average Milestone Progress      Not Measured    console log ToArray GoalProgressMeasurements

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function enumKeys  enum      const entries   Object entries  enum  filter e   gt   isNaN Number e 0        if   entries length           enum has string values so we can use Object keys     return Object keys  enum         return entries map e   gt  e 1

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Simply this will return an array of enum values   Object values myEnum

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I don t think the order can be guaranteed  otherwise it would be easy enough to slice the second half of Object entries result and map from there  The only  very minor  issues with the answers above is that  there is a lot of unnecessary type conversion between string and number  the entries are iterated twice when a single iteration is just as clean and effective   type StandardEnum      id  string   number   string   nu  number   string    function enumToList lt T extends StandardEnum gt   enm  T      id  number  description  string           return Object entries enm  reduce  accum  kv    gt            if  typeof kv 1       number                 accum push   id  kv 1   description  kv 0                       return accum               if enum is huge  perhaps pre-allocate with new Array entries length   2   however then push won t work  so tracking an index would also be required

User · Answer

You can do that in this way   export enum GoalProgressMeasurements       Percentage   1      Numeric Target   2      Completed Tasks   3      Average Milestone Progress   4      Not Measured   5    export class GoalProgressMeasurement       constructor public goalProgressMeasurement  GoalProgressMeasurements  public name  string             export var goalProgressMeasurements     key  number   GoalProgressMeasurement           1  new GoalProgressMeasurement GoalProgressMeasurements Percentage   Percentage        2  new GoalProgressMeasurement GoalProgressMeasurements Numeric Target   Numeric Target        3  new GoalProgressMeasurement GoalProgressMeasurements Completed Tasks   Completed Tasks        4  new GoalProgressMeasurement GoalProgressMeasurements Average Milestone Progress   Average Milestone Progress        5  new GoalProgressMeasurement GoalProgressMeasurements Not Measured   Not Measured        And you can use it like this   var gpm  GoalProgressMeasurement   goalProgressMeasurements GoalProgressMeasurements Percentage   var gpmName  string   gpm name   var myProgressId  number   1     the value can come out of drop down selected value or from back-end   so you can imagine the way of using var gpm2  GoalProgressMeasurement   goalProgressMeasurements myProgressId   var gpmName  string   gpm name    You can extend the GoalProgressMeasurement with additional properties of the object as you need  I m using this approach for every enumeration that should be an object containing more then a value

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Easy Solution  You can use the following function to convert your Enum to an array of objects     buildGoalProgressMeasurementsArray    Object          return Object keys GoalProgressMeasurements                 map key   gt     id  GoalProgressMeasurements key   name  key          If you needed to strip that underscore off  we could use regex as follows   buildGoalProgressMeasurementsArray    Object          return Object keys GoalProgressMeasurements                 map key   gt     id  GoalProgressMeasurements key   name  key replace    g

[javascript] TypeScript enum to object array

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