How do I convert a string to enum in TypeScript

Question

I have defined the following enum in TypeScript   enum Color      Red  Green     Now in my function I receive color as a string  I have tried the following code   var green   Green   var color   Color    lt Color gt green     Error  can t convert string to enum   How can I convert that value to an enum

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Try this      var color   Color    Color as any   Green     That works fine for 3 5 3 version

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Enums created in the way you did are compiled into an object that stores both forward  name - gt  value  and reverse  value - gt  name  mappings  As we can observe from this chrome devtools screenshot     Here is an example of how dual mapping works and how to cast from one to another   enum Color      Red  Green      To Number var greenNr  number   Color  Green    console log greenNr      logs 1     To String var greenString  string   Color Color  Green         or Color Color 1  console log greenString      logs Green     In your example     recieve as Color green instead of the string green var green  string   Color Color Green         obtain the enum number value which corresponds to the Color green property var color  Color     lt any gt Color  green      console log color      logs 1

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Given you use typescript  Many of the solutions above might not work or are overly complex  Situation  The strings are not the same as the enum values  casing differs  enum Color     Green    quot green quot     Red    quot red quot     Just use  const color    quot green quot  as Color  Please note that this does not guarantee a valid enum

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Simplest approach enum Color   Red  Green    const c1   Color  quot Red quot   const redStr    quot Red quot     important  use  const   not mutable  let  const c2   Color redStr   This works both for numeric and string enums  No need to use a type assertion  Unknown enum strings Simple  unsafe variant const redStrWide  string    quot Red quot     wide  unspecific typed string const c3   Color redStrWide as keyof typeof Color   Safe variant with checks const isEnumName    lt T gt  str  string   enum  T   str is Extract lt keyof T  string gt    gt      str in  enum const enumFromName    lt T gt  name  string   enum  T    gt        if   isEnumName name   enum   throw Error      here fail fast as an example     return  enum name    const c4   enumFromName redStrWide  Color   Convert string enum values String enums don t have a reverse mapping  in contrast to numeric ones   We can create a lookup helper to convert an enum value string to an enum type  enum ColorStr   Red    quot red quot   Green    quot green quot     const c5 by name   ColorStr  quot Red quot        this works const c5 by value error   ColorStr  quot red quot          but this not  const enumFromValue    lt T extends Record lt string  string gt  gt  val  string   enum  T    gt        const enumName    Object keys  enum  as Array lt keyof T gt   find k   gt   enum k      val      if   enumName  throw Error      here fail fast as an example     return  enum enumName     const c5   enumFromValue  quot red quot   ColorStr   Playground sample

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I also ran into the same compiler error   Just a slight shorter variation of Sly cardinal s approach   var color  Color   Color  lt string gt colorId

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I needed to know how to loop over enum values  was testing lots of permutations of several enums  and I found this to work well   export enum Environment       Prod    http   asdf com       Stage    http   asdf1234 com       Test    http   asdfasdf example com     Object keys Environment  forEach  environmentKeyValue    gt        const env   Environment environmentKeyValue as keyof typeof Environment         env is now equivalent to Environment Prod  Environment Stage  or Environment Test     Source  https   blog mikeski net development javascript typescript-enums-to-from-string

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Typescript 3 9 propsal enum Color  RED  GREEN    const color    RED  as Color   easy peasy    lemon squeezy

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Enum   enum MyEnum       First      Second      Three     Sample usage  const parsed   Parser parseEnum  FiRsT   MyEnum      parsed   MyEnum First   const parsedInvalid  Parser parseEnum  other   MyEnum      parsedInvalid   undefined   Ignore case sensitive parse   class Parser       public static parseEnum lt T gt  value  string  enumType  T   T keyof T    undefined           if   value                return undefined                     for  const property in enumType                const enumMember   enumType property               if  typeof enumMember      string                     if  enumMember toUpperCase       value toUpperCase                          const key   enumMember as string as keyof typeof enumType                      return enumType key                                                     return undefined

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If you provide string values to your enum  a straight cast works just fine   enum Color     Green    Green     Red    Red     const color    Green   const colorEnum   color as Color

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Enums in TypeScript 0 9 are string number based  You should not need type assertion for simple conversions    enum Color      Red  Green       To String  var green  string   Color Color Green       To Enum   number var color   Color   Color green     Try it online  I have documention about this and other Enum patterns in my OSS book   https   basarat gitbook io typescript type-system enums

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If you are sure that an input string has an exact match with Color enum then use   const color  Color     lt any gt Color   Red      In the case where an input string may not match Enum  use   const mayBeColor  Color   undefined     lt any gt Color   WrongInput    if  mayBeColor     undefined           TypeScript will understand that mayBeColor is of type Color here     Playground    If we do not cast enum to  lt any gt  type then TypeScript will show the error      Element implicitly has  any  type because index expression is not of type  number     It means that by default the TypeScript Enum type works with number indexes  i e  let c   Color 0   but not with string indexes like let c   Color  string    This is a known restriction by the Microsoft team for the more general issue Object string indexes

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enum Color      Red  Green       To String  var green  string   Color Color Green       To Enum   number var color   Color   Color green as keyof typeof Color     Works with --noImplicitAny   This example works with --noImplicitAny in TypeScript  Sources  https   github com Microsoft TypeScript issues 13775 issuecomment-276381229 https   www typescriptlang org docs handbook advanced-types html index-types

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other variation can be    const green   Green    const color   Color   Color green  as Color

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I was looking for an answer that can get an enum from a string  but in my case  the enums values had different string values counterpart   The OP had a simple enum for Color  but I had something different   enum Gender     Male    Male     Female    Female     Other    Other     CantTell    Can t tell      When you try to resolve Gender CantTell with a  Can t tell  string  it returns undefined with the original answer   Another answer  Basically  I came up with another answer  strongly inspired by this answer   export const stringToEnumValue    lt ET  T gt  enumObj  ET  str  string   T   gt     enumObj as any  Object keys enumObj  filter k   gt   enumObj as any  k      str  0      Notes   We take the first result of filter  assuming the client is passing a valid string from the enum   If it s not the case  undefined will be returned  We cast enumObj to any  because with TypeScript 3 0   currently using TypeScript 3 5   the enumObj is resolved as unknown    Example of Use  const cantTellStr    Can t tell    const cantTellEnumValue   stringToEnumValue lt typeof Gender  Gender gt  Gender  cantTellStr   console log cantTellEnumValue      Can t tell   Note  And  as someone pointed out in a comment  I also wanted to use the noImplicitAny   Updated version  No cast to any and proper typings   export const stringToEnumValue    lt T  K extends keyof T gt  enumObj  T  value  string   T keyof T    undefined   gt    enumObj Object keys enumObj  filter  k    gt  enumObj k as K  toString       value  0  as keyof typeof enumObj     Also  the updated version has a easier way to call it and is more readable   stringToEnumValue Gender   Can t tell

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I got it working using the following code   var green   Green   var color   Color   lt Color gt Color green

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If the TypeScript compiler knows that the type of variable is string then this works   let colorName   string    Green   let color   Color   Color colorName     Otherwise you should explicitly convert it to a string  to avoid compiler warnings    let colorName   any    Green   let color   Color   Color      colorName     At runtime both solutions will work

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There s a lot of mixed information in this question  so let s cover the whole implementation for TypeScript 2 x  in Nick s Guide to Using Enums in Models with TypeScript   This guide is for  people who are creating client-side code that s ingesting a set of known strings from the server that would be conveniently modeled as an Enum on the client side   Define the enum  Let s start with the enum  It should look something like this   export enum IssueType     REPS    REPS     FETCH    FETCH     ACTION    ACTION     UNKNOWN    UNKNOWN       Two thing of note here    We re explicitly declaring these as string-backed enum cases which allows us to instantiate them with strings  not some other unrelated numbers  We ve added an option that may or may not exist on our server model  UNKNOWN  This can be handled as undefined if you prefer  but I like to avoid   undefined on types whenever possible to simplify handling    The great thing about having an UNKNOWN case is that you can be really obvious about it in code and make styles for unknown enum cases bright red and blinky so you know you re not handling something correctly   Parse the enum  You might be using this enum embedded in another model  or all alone  but you re going to have to parse the string-y typed enum from JSON or XML  ha  into your strongly typed counterpart  When embedded in another model  this parser lives in the class constructor   parseIssueType typeString  string   IssueType     const type   IssueType typeString     if  type     undefined        return IssueType UNKNOWN         return type      If the enum is properly parsed  it ll end up as the proper type  Otherwise  it ll be undefined and you can intercept it and return your UNKNOWN case  If you prefer using undefined as your unknown case  you can just return any result from the attempted enum parsing   From there  it s only a matter of using the parse function and using your newly strong typed variable   const strongIssueType  IssueType   parseIssueType  ACTION       IssueType ACTION const wrongIssueType  IssueType   parseIssueType  UNEXPECTED       IssueType UNKNOWN

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If you are using namespaces to extend the functionality of your enum then you can also do something like      enum Color           Red  Green            export namespace Color         export function getInstance color  string    Color           if color     Red               return Color Red            else if  color     Green               return Color Green                            and use it like this    Color getInstance  Red

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If you re interested in type guarding an what would otherwise be a string  which is how I came across this issue   this might work for you  enum CurrencyCode     cad    quot cad quot     eur    quot eur quot     gbp    quot gbp quot     jpy    quot jpy quot     usd    quot usd quot      const createEnumChecker    lt T extends string  TEnumValue extends string gt     enumVariable     key in T   TEnumValue       gt      const enumValues   Object values enumVariable     return  value  string   number   boolean   value is TEnumValue   gt      enumValues includes value       const isCurrencyCode   createEnumChecker CurrencyCode    const input  string    gbp    let verifiedCurrencyCode  CurrencyCode   null   null     verifiedCurrencyCode   input       TypeError  Type  string  is not assignable to type  CurrencyCode   null    if  isCurrencyCode input       verifiedCurrencyCode   input     No Type Error      Solution is taken from this github issue discussing generic Enums

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This note relates to basarat s answer  not the original question     I had an odd issue in my own project where the compiler was giving an error roughly equivalent to  cannot convert string to Color  using the equivalent of this code   var colorId   myOtherObject colorId     value  Green   var color  Color    lt Color gt Color colorId      TSC error here  Cannot convert string to Color    I found that the compiler type inferencing was getting confused and it thought that colorId was an enum value and not an ID  To fix the problem I had to cast the ID as a string   var colorId    lt string gt myOtherObject colorId     Force string value here var color  Color   Color colorId      Fixes lookup here    I m not sure what caused the issue but I ll leave this note here in case anyone runs into the same problem I did

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For TS 3 9 x var color   Color   Color green as unknown as keyof typeof Color

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As of Typescript 2 1 string keys in enums are strongly typed  keyof typeof is used to get info about available string keys  1    enum Color      Red  Green    let typedColor  Color   Color Green  let typedColorString  keyof typeof Color    Green       Error  Black is not assignable       indexing using Color  Black   will return undefined runtime  typedColorString    Black       Error  Type  string  is not assignable       indexing works runtime  let letColorString    Red   typedColorString   letColorString      Works fine typedColorString    Red       Works fine const constColorString    Red   typedColorString   constColorString     Works fine  thanks  SergeyT  let letColorString    Red   typedColorString   letColorString as keyof typeof Color   typedColor   Color typedColorString     https   www typescriptlang org docs handbook advanced-types html index-types

[typescript] How do I convert a string to enum in TypeScript?

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