What is Enum

In TypeScript, an enum (short for “enumeration”) is a way to define a set of named constants. Enums allow you to create a collection of related values that can be numeric or string-based. They are useful for representing a set of discrete values, such as days of the week, months of the year, or status codes.

Types of Enums

TypeScript supports two types of enums: numeric and string.

Numeric Enums

Numeric enums are the default type of enums in TypeScript. The first value in a numeric enum has a default value of 0, and each subsequent value is incremented by 1.

enum Direction {
  Up,
  Down,
  Left,
  Right
}

let directionUp: Direction = Direction.Up;
let directionRight: Direction = Direction.Right;
console.log(directionUp); // Outputs: 0
console.log(directionRight); // Outputs: 3

You can also specify custom numeric values for the enum members:

enum Direction {
  Up = 1,
  Down,
  Left = 5,
  Right
}

console.log(Direction.Up);    // Outputs: 1
console.log(Direction.Down);  // Outputs: 2
console.log(Direction.Left);  // Outputs: 5
console.log(Direction.Right); // Outputs: 6

String Enums

String enums are enums where each member has a string value. They provide a clearer and more readable way to define enum values.

enum Direction {
  Up = "UP",
  Down = "DOWN",
  Left = "LEFT",
  Right = "RIGHT"
}

let direction: Direction = Direction.Up;
console.log(direction); // Outputs: "UP"

Using enum in switch case

Enums can be used to define and check for specific values within a set.

enum Status {
  New,
  InProgress,
  Completed
}

function updateStatus(status: Status): void {
  switch (status) {
    case Status.New:
      console.log("Starting new task.");
      break;
    case Status.InProgress:
      console.log("Task is in progress.");
      break;
    case Status.Completed:
      console.log("Task is completed.");
      break;
  }
}

updateStatus(Status.InProgress); // Outputs: "Task is in progress."