getEnumKey function

Finds the member name of an enum value, string enums included: a readable name for a log or a translation key.

import { getEnumKey } from 'utils';

Signature

export function getEnumKey<E extends EnumObject>(enumObject: E, value: unknown): (keyof E & string) | undefined

Parameters

Name	Description
E	The type of the enum object.
enumObject	The enum, such as Status.
value	The value to name.

Returns

The first member name with this value; undefined when none has it.

Example

enum Status { Idle = 'idle', Running = 'running' }
getEnumKey(Status, 'running'); // 'Running'

Tests

Line coverage: 100 %.

• ✅ names the value of a string or numeric enum
• ✅ returns undefined for a value outside the enum

Source

src/enum/get-enum-key.ts (on GitHub)

Uses

• EnumObject: Any TypeScript enum, or a const object used as one.
• getEnumEntries: Lists the members of an enum as [name, value] pairs, without the reverse mapping of numeric enums.

Files it needs

src/enum/get-enum-key.ts imports, directly or not:

• src/enum/enum-object.ts
• src/enum/get-enum-entries.ts

Source code

import type { EnumObject } from './enum-object';
import { getEnumEntries } from './get-enum-entries';

/**
 * Finds the member name of an enum value, string enums included: a readable name for a log or a
 * translation key.
 *
 * @template E - The type of the enum object.
 * @param enumObject - The enum, such as `Status`.
 * @param value - The value to name.
 * @returns The first member name with this value; `undefined` when none has it.
 * @example
 * enum Status { Idle = 'idle', Running = 'running' }
 * getEnumKey(Status, 'running'); // 'Running'
 */
export function getEnumKey<E extends EnumObject>(enumObject: E, value: unknown): (keyof E & string) | undefined {
  return getEnumEntries(enumObject).find(([, member]) => member === value)?.[0];
}

Test file

import { getEnumKey } from './get-enum-key';

enum Status {
  Idle = 'idle',
  Running = 'running',
}

enum Level {
  Low = 0,
  High = 1,
}

describe(getEnumKey, () => {
  it('names the value of a string or numeric enum', () => {
    expect(getEnumKey(Status, 'running')).toBe('Running');
    expect(getEnumKey(Level, 1)).toBe('High');
  });

  it('returns undefined for a value outside the enum', () => {
    expect(getEnumKey(Status, 'stopped')).toBeUndefined();
    expect(getEnumKey(Level, '1')).toBeUndefined();
  });
});

Keywords: get, enum, key, enums, function