How to check the type is enum or not in typescript

Question

I have a string enum type like:

export enum UserRole {
admin = "admin",
active = "active",
blocked = "blocked"
}

I

Answer 1

The value of an enum is either a string or number. So, they only way to test, is to test against a string or number.

We can start by creating a User-Defined Type Guard which would look like this:

function isInstance(value: string, type: T): type is T {
    return Object.values(type).includes(value)
}

This returns true or false if the value is found in the enum (This doesn't work well on numbers or enums with the same string).

enum Animal {
    Cat = 'cat',
    Dog = 'dog'
}

enum Plant {
    Tree = 'tree',
    Flower = 'flower'
}

function isInstance(value: string | number, type: T): type is T {
    return Object.values(type).includes(value)
}

console.log(isInstance('dog', Animal)) // True
console.log(isInstance('dog', Plant))  // False