Get TypeScript enum name from instance

Question

I have the following TypeScript enum:

enum Country {
    BR = "Brazil",
    NO = "Norway"
}

Then imagine I have a method that takes a Country as an argument, like so:

someFunc = (country: Country): void => {
    console.log(country) //Will print "Brazil" if country = Country.BR
    console.log(Country[country]) //Same as above
    console.log(???) //I want to print "BR" if country = Country.BR
}

How do I solve the third console.log statement?

How do I get a hold of the enum key?

Regards

Suren Srapyan · Accepted Answer · 2018-01-16 07:40:21Z

18

Under the enum constrution you get something like this

Country["BR"] = "Brazil";
Country["NO"] = "Norway";

which is a simple object.

By default you can't get the keys of your enum. But you can iterate over the keys manually and try to find that one.

enum Country {
    BR = "Brazil",
    NO = "Norway"
}

console.log(Object.keys(Country).find(key => Country[key] === country))

edited Jan 16, 2018 at 7:40

answered Jan 16, 2018 at 7:39

Suren Srapyan

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5 Comments

Robin Jonsson Over a year ago

But that means making an if statement for all possible values?

Suren Srapyan Over a year ago

Why if statements? You can just compare with your country

Robin Jonsson Over a year ago

It's not very flexible... Say I have 100 enum values inside my Country enum, and my method would like to print the country code (key of the enum) for a given enum instance. Then there's no solution for this?

Suren Srapyan Over a year ago

Country[key] === country) this statement will work for every country. It just gets the key of that enum. If I understood you correct.

Robin Jonsson Over a year ago

Ah yes, that works indeed! Was hoping there was a more simple solution for this

Jeff Lau · Accepted Answer · 2018-02-24 06:43:06Z

4

ts-enum-util (github, npm) supports reverse lookup of value->key for string enums, compile time type safety, and run-time validation.

import {$enum} from "ts-enum-util";

enum Country {
    BR = "Brazil",
    NO = "Norway"
}

someFunc = (country: Country): void => {
    // throws an error if the value of "country" at run time is
    // not "Brazil" or "Norway".  
    // type of "name": ("BR" | "NO")
    const name = $enum(Country).getKeyOrThrow(country);
}

answered Feb 24, 2018 at 6:43

Jeff Lau

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Comments

Dhruv Pal · Accepted Answer · 2022-05-08 13:45:33Z

First you need to understand what is the js code for

enum Country {
    BR = "brazil",
    NO = "norway"
}

Its simply

var Country;
(function (Country) {
    Country["BR"] = "brazil";
    Country["NO"] = "norway";
})(Country || (Country = {}));

So basically it's an object with "BR" and "NO" as keys. and assuming we know how to find key from value in object. Check this . Using same

enum Country {
    BR = "brazil",
    NO = "norway"
}

namespace Country {
    export function getEnum(c: string): Country | undefined {
        if(!c) return undefined;
        const cLowerCase = c.toLowerCase();
        return Object.keys(Country).find(k => Country[k as keyof typeof Country] === cLowerCase) as Country
    }
}


console.log(Country.getEnum('test'))

console.log(Country.getEnum('Brazil'))

console.log(Country.getEnum('norway'))

If you are wondering why we used keyof typeof check this answer

In case you have lots of keys in enum you can use map to store reverse mapping and use that

Guillermo Ruffino · Accepted Answer · 2023-10-19 18:28:09Z

0

I made this "generic" version


enum AccountType {
  Google = 'goo',
  Local = 'cal',
  Facebook = 'boo',
  Twitter = 'x',
  LinkedIn = 'ink'
}

function getEnumName<T> (enumType: Record<string, number|string>, value: T) {
  return Object.entries(enumType).find(([k,v] ) =>  v === value )?.[0];
}
 
console.log(getEnumName(AccountType, AccountType.Twitter));

answered Oct 19, 2023 at 18:28

Guillermo Ruffino

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Comments

Robert Penner · Accepted Answer · 2018-01-17 03:15:25Z

-1

I often use a plain JavaScript object instead of an enum, and use the keyof operator for type safety on its keys:

const CountryMap = {
    BR: "Brazil",
    NO: "Norway"
};

// equivalent to: type Country = 'BR' | 'NO';
type Country = keyof typeof CountryMap;

const someFunc = (country: Country): void => {
    console.log(country);
}

answered Jan 17, 2018 at 3:15

Robert Penner

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