Get key of an enum from its value in typescript

Question

I have the following enum

export enum Operators {
    Equal = "1",
    NotEqual = "2",
    GreatherOrEqual = "3",
    LessOrEqual = "4",
    Contains = "5",
    Null = "6",
    NotNull = "7",
    Between = "8",
    StartsWith = "9",
    EndsWith = "10"
}

I need to recover the enum key from the value that is stored. I have created the following:

GetEnumTextByValue ( valueOperator: string ): string {
    const values: string[] = Object.values( Operators ).filter( v => v == v );
    const keys: string[] = Object.keys( Operators ).filter( k => k == k );
    const index: number = values.indexOf( valueOperator );
    return keys[ index ];
}

The function returns what I need, but is there any simpler way to get the key?

You could use Object.entries(Operators). It returns an array of [ key, value ] — Paul Cosma
– Paul Cosma, Commented May 22, 2019 at 20:00

Nux · Accepted Answer · 2020-06-14 18:47:25Z

2

I am using this function for any enum

export function getEnumKeyByEnumValue(myEnum: any, enumValue: number | string): string {
  let keys = Object.keys(myEnum).filter((x) => myEnum[x] == enumValue);
  return keys.length > 0 ? keys[0] : '';
}

Tests using jest

describe('enum', () => {
  enum TestEnumWithNumber {
    ZERO
  }

  enum TestEnumWithString {
    ZERO = 'ZERO'
  }

  it('should return correct key when enum has number values', function () {
    const key = getEnumKeyByEnumValue(TestEnumWithNumber, TestEnumWithNumber.ZERO);
    expect(key).toBe('ZERO');
  });

  it('should return correct key when enum has string values', function () {
    const key = getEnumKeyByEnumValue(TestEnumWithString, TestEnumWithString.ZERO);
    expect(key).toBe('ZERO');
  });
});

answered Jun 14, 2020 at 18:47

Nux

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Comments

Karol Majewski · Accepted Answer · 2020-06-14 21:04:02Z

2

You can use a combination of Object.entries and a Map:

const operators = new Map(
  Object.entries(Operators)
    .map(entry => entry.reverse()) as [Operators, keyof typeof Operators][]
);

console.log(
  operators.get(Operators.Between) // Between
)

Note that this is way easier to do when your enum contains numbers instead of strings.

export enum Operators {
    Equal = 1,
    NotEqual = 2,
    GreatherOrEqual = 3,
    LessOrEqual = 4,
    Contains = 5,
    Null = 6,
    NotNull = 7,
    Between = 8,
    StartsWith = 9,
    EndsWith = 10
}

Operators[Operators.Between]; // "Between"

edited Jun 14, 2020 at 21:04

answered Jun 14, 2020 at 19:12

Karol Majewski

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Comments

edu · Accepted Answer · 2019-05-22 20:27:31Z

1

Perfect. Thank you Paul. I have modified it in the following way:

GetEnumTextByValue ( valueOperator: string ): string {
    let operator: string;
    for ( let [ key, value ] of Object.entries( Operators ) ) {
        value === valueOperator ? operator = key : null;
    }
    return operator;
}

answered May 22, 2019 at 20:27

edu

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