Union Type and Enum

we usually use Enum or union type using typescript.

they are defined sets of values in programming, but they serve different purposes.

Today, we are going to find out about these.

we can make a similar type using those two type.

union type

a union type is a type can hold one of several types.

type DeviceType = "phone" | "pad" | "deskTop"

enum

An enumm defines a set of named values.

enum DeviceType {
phone="phone",
pad="pad",
deskTop="deskTop"
}

what is the difference between them?

1. Enum is impossible to extend. if we need to combine types, we should use union type.

enum Fruit {
APPLE,
BANANA
}

enum AnotherFruit{
PINEAPPLE
}

type Fruit = Fruit | AnotherFruit

2. Enum can not allocate the value directly.

enum Fruit {
APPLE = 'APPLE',
BANANA = "BANANA"
}

getSomeFruit('APPLE') // X
getSomeFruit(Fruit.APPLE) // O

3. Numberic enum in enum is not guarantee type stability.

enum Status{
pedding=0,
success=1,
fail=2
}

const newStatus: Status = 100; // none error here..

4. The size of an enum is larger than that of a union type.

In most cases, an Enum can be replaced by union type.

and an Enum an be replaced by object also.

const Device = {
phone="phone",
pad="pad",
deskTop="deskTop"
} as const

type DeviceType = typeof Device[keyof typeof Device]

When can we use an enum?

Reverse mapping

enum Color {
    Red = 1,
    Green,
    Blue
}

// Forward mapping
console.log(Color.Red); // Output: 1
console.log(Color.Green); // Output: 2

// Reverse mapping
console.log(Color[1]); // Output: "Red"
console.log(Color[2]); // Output: "Green"