An enum is a special "class" that represents a group of constants (unchangeable variables).
Enums come in two flavors string and numeric .
Let's start with numeric.
Numeric Enums - Default
By default, enums will initialize the first value to 0 and add 1 to each additional value:
Example
enum CardinalDirections {
North, East, South, West
}
let currentDirection = CardinalDirections.North;
// logs 0 console.log(currentDirection); // throws error as 'North' is not a valid enum currentDirection = 'North'; // Error: "North" is not assignable to type 'CardinalDirections'.Numeric Enums - Initialized
You can set the value of the first numeric enum and have it auto increment from that:
Example
enum CardinalDirections {
North = 1, East, South, West
}
// logs 1 console.log(CardinalDirections.North); // logs 4 console.log(CardinalDirections.West);Numeric Enums - Fully Initialized
You can assign unique number values for each enum value.
Then the values will not be incremented automatically:
Example
enum StatusCodes {
NotFound = 404, Success = 200, Accepted = 202, BadRequest = 400
}
// logs 404 console.log(StatusCodes.NotFound); // logs 200 console.log(StatusCodes.Success);String Enums
Enums can also contain strings .
This is more common than numeric enums, because of their readability and intent.
Example
enum CardinalDirections {
North = 'North', East = "East", South = "South", West = "West"
};
// logs "North" console.log(CardinalDirections.North); // logs "West" console.log(CardinalDirections.West);Technically, you can mix and match string and numeric enum values, but it is recommended not to do so.