9. Enum

An enum is a way to define a set of named constants that can be used as a type.

Example 1: Default Numeric Enum

By default, enum members are assigned incrementing numeric values starting from 0.

enum Color {
  Red,    // 0
  Green,  // 1
  Blue    // 2
}
 
let c: Color = Color.Green;  // c = 1

Example 2: Custom Numeric Values

You can manually assign values to enum members.

enum Color {
  Red = 1,    // 1
  Green,      // 2
  Blue        // 3
}
 
let c: Color = Color.Green;  // c = 2

Example 3: Enum with Specific Values

You can also set custom values for each enum member.

enum Color {
  Red = 1,    // 1
  Green = 2,  // 2
  Blue = 4    // 4
}
 
let c: Color = Color.Green;  // c = 2

Accessing Enum by Value

You can access the name of the enum member by its value.

let colorName: string = Color[2];  // "Green"
console.log(colorName);  // Displays 'Green'

Key Points:

1. Numeric Enum: Enum values are automatically assigned starting from 0 unless specified.
2. Custom Values: You can manually assign values to each enum member.
3. Accessing by Value: You can retrieve the name of an enum member using its numeric value (reverse lookup).