TypeScript Enums
Enums (Enumerations) allow you to define a set of named constants. Using enums can make it easier to document intent or create a set of distinct cases. TypeScript provides both numeric and string-based enums.
1. Numeric Enums
By default, enums are number-based. They start at zero and increment by 1 for each member.
enum Direction {
Up, // 0
Down, // 1
Left, // 2
Right // 3
}
let move: Direction = Direction.Up;You can also initialize the first member, and the rest will auto-increment from there.
enum Direction {
Up = 1,
Down, // 2
Left, // 3
Right // 4
}Reverse Mapping
Numeric enums support reverse mapping. You can access the name of the enum member using its value.
console.log(Direction[1]); // Output: "Up"2. String Enums
String enums allow you to give a meaningful string value to each member. They do not have auto-incrementing behavior, but they are easier to debug because the value is readable at runtime.
enum Status {
Success = "SUCCESS",
Failure = "FAILURE",
Pending = "PENDING"
}
if (response.status === Status.Success) {
console.log("Operation worked!");
}3. Enums vs Union Types
A common alternative to Enums is using Union Types with string literals.
// Enum approach
enum LogLevel {
Error,
Warning,
Info
}
// Union Type approach
type LogLevelType = "Error" | "Warning" | "Info";When to use which?
- Use Enums if you need to iterate over the values or need a mapping between keys and values (like a dropdown list).
- Use Union Types for simple string constants, as they are lighter weight and compile away completely in JavaScript.