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Mastering TypeScript

Enums

Explore TypeScript enums to define human-readable names for numeric or string values. Understand standard enums, string enums, and const enums, and how they help eliminate magic numbers while improving code clarity and performance.

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Introduction to enums

Enums are a special type whose concept is similar to other languages, such as C#, C++, or Java, and provides the solution to the problem of special numbers or special strings.

Enums are used to define a human-readable name for a specific number or string.

Consider the following code:

TypeScript 4.9.5
// Define an enum with the values 'Open' and 'Closed'
enum DoorState {
  Open,
  Closed
}
// Declare a function that takes an argument of type 'DoorState'
function checkDoorState(state: DoorState) {
  // Print the enum value to the console
  console.log(`enum value is : ${state}`);
  // Use a switch statement to check the value of 'state'
  switch (state) {
    // If 'state' is 'Open', print a message to the console
    case DoorState.Open:
      console.log(`Door is open`);
      break;
    // If 'state' is 'Closed', print a message to the console
    case DoorState.Closed:
      console.log(`Door is closed`);
      break;
  }
}
Defining enum DoorState

  • We start by using the enum keyword to define an enum named DoorState on line 2. This enum has two possible values, either Open or Closed.

  • We then have a function named checkDoorState on lines 8–23 that has a single parameter named state of type DoorState. This means that the ...