How to get a random enum in TypeScript?

Question

How to get a random item from an enumeration?

enum Colors {
  Red, Green, Blue
}

function getRandomColor(): Color {
  // return a random Color (Red, Green, Blue) here
}

Answer 1

After much inspiration from the other solutions, and the keyof keyword, here is a generic method that returns a typesafe random enum.

function randomEnum<T>(anEnum: T): T[keyof T] {
  const enumValues = Object.keys(anEnum)
    .map(n => Number.parseInt(n))
    .filter(n => !Number.isNaN(n)) as unknown as T[keyof T][]
  const randomIndex = Math.floor(Math.random() * enumValues.length)
  const randomEnumValue = enumValues[randomIndex]
  return randomEnumValue;
}

Use it like this:

interface MyEnum {X, Y, Z}
const myRandomValue = randomEnum(MyEnum) 

myRandomValue will be of type MyEnum.

Answer 2

Most of the above answers are returning the enum keys, but don't we really care about the enum values?

If you are using lodash, this is actually as simple as:

_.sample(Object.values(myEnum)) as MyEnum

The casting is unfortunately necessary as this returns a type of any. :(

If you're not using lodash, or you want this as its own function, we can still get a type-safe random enum by modifying @Steven Spungin's answer to look like:

function randomEnum<T>(anEnum: T): T[keyof T] {
  const enumValues = (Object.values(anEnum) as unknown) as T[keyof T][];
  const randomIndex = Math.floor(Math.random() * enumValues.length);
  return enumValues[randomIndex];
}