In Typescript, an enum (enumeration) is a way to create a named set of named constant values.
Enums allow us to define a set of related named constants, making our code more readable and self-explanatory.
Enums are helpful when we have a set of values that are related and known at compile time.
Enum Support Reverse Mapping: Enums support reverse mapping, we can access the enum member attribute from its value.
Assign Auto Numbering: By default, Enums are automatically assigned numeric values starting from 0. We can also assign specific string values or numeric values to enum members.
Support Named Constants: Enums allow us to define a set of named constants that can be easily referenced throughout our code.
Numeric enums are enums where each member has an associated numeric value.
enum Direction {
UP, // 0
DOWN, // 1
LEFT, // 2
RIGHT // 3
}
let arrowButtonPress: Direction = Direction.RIGHT;
console.log(arrowButtonPress); // Output: 3
Direction is an enum with default numeric values starting from 0. we can explicitly set values as well.
enum Permission {
ADMIN = "Admin",
SUPER_ADMIN = "Super Admin",
IAM = "Iam"
}
let selectedPermission: Permission = Permission.ADMIN;
console.log(selectedPermission); // Output: "Admin"
String enums are enums where each member has an associated string value.
Permission is an enum with string values assigned to each member.
enum Months {
JAN = 1,
FEB = "feb",
MAR = "mar",
APR = "apr",
MAY = 5,
JUNE = 6
}
let selectedMonth: Months = Months.APR;
console.log(selectedMonth); // Output: "apr"
enum StatusCode {
OK = 200,
BadRequest = 400,
NotFound = 404,
InternalServerError = 500
}
let responseCode: StatusCode = StatusCode.OK;
console.log(responseCode); // Output: 200
Heterogeneous enums allow a mix of string and numeric values.
enum Months {
JAN = 1,
FEB = "feb",
MAR = "mar",
APR = "apr",
MAY = 5,
JUNE = 6
}
let month: string = Months[0]; // Accessing enum value by numeric value
console.log(month); // Output: 1
enum StatusCode {
OK = 200,
BadRequest = 400,
NotFound = 404,
InternalServerError = 500
}
let statusCode: string = StatusCode["OK"]; // Accessing enum value by string value
console.log(statusCode); // Output: 200
We can explicitly set numeric values for each member.
We can access the values of an enum using the enum name and the member name.