TypeScript Enums
An enum is a special "class" that represents a group of constants (unchangeable variables).
Enums come in two flavors string and numeric. Lets 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'.
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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);
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Numeric Enums - Fully Initialized
You can assign unique number values for each enum value. Then the values will not 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);
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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);
Try it Yourself »
Technically, you can mix and match string and numeric enum values, but it is recommended not to do so.
