1. Definition of Enums

   • Basic Syntax: Enums are defined using the enum keyword followed by the name of the enum and its members enclosed in curly braces.

     enum Direction {
        Up,
        Down,
        Left,
        Right
     }

2. Numeric Enums

   • Default Numeric Enums: By default, enums start at 0 and increment by 1 for each subsequent member.

     enum CardinalDirections {
        North, // 0
        East, // 1
        South, // 2
        West // 3
     }

   • Initialized Numeric Enums: You can specify the starting value for an enum.

     enum CardinalDirections {
        North = 1, // Starts from 1
        East, // 2
        South, // 3
        West // 4
     }

   • Fully Initialized Numeric Enums: You can assign specific values to each member.

     enum StatusCodes {
        NotFound = 404,
        Success = 200,
        Accepted = 202,
        BadRequest = 400
     }
     
     console.log(StatusCodes.NotFound); // Outputs: 404

3. String Enums

   • String enums allow you to define enums with string values ​​instead of numeric values. This is often preferred for readability.
     

     enum CardinalDirections {
        North = "North",
        East = "East",
        South = "South",
        West = "West"
     }
     
     console.log(CardinalDirections.North); // Outputs: "North"

4. Heterogeneous Enums

   • Mixing Types: You can mix string and numeric values ​​in an enum, although this is generally not recommended for clarity.

     enum MixedEnum {
        No = "No",
        Yes = "Yes",
        Maybe = 2 // Numeric value mixed with strings
     }

5. Reverse Mapping:

   • Accessing Enum Members: Numeric enums support reverse mapping, which allows you to get the name of an enum member from its value.
     

     enum CardinalDirections {
        North = 1,
        East,
        South,
        West
     }
     
     console.log(CardinalDirections[1]); // Outputs: "North"

   • Limitations with String Enums: String enums do not support reverse mapping because their values ​​are not unique.
     

     enum CardinalDirections {
        North = "North",
        East = "East"
     }
     
     // console.log(CardinalDirections["North"]); // Error: Cannot access string enums this way.

6. Computed and Constant Members

   • Constant Members: These are initialized with constant expressions that can be evaluated at compile time.

     const constantValue = 10;
     
     enum ExampleEnum {
        A = constantValue, // Error: computed value must be constant.
        B = constantValue + 5 // Error: computed value must be constant.
     }

7. Ambient Enums

   • Ambient Enums: These are used to describe the shape of an existing enum that is defined elsewhere (eg in a library).

     declare enum AmbientEnum {
        A,
        B,
        C
     }

Conclusion

• Enums in TypeScript provide a way to create named constants that improve code clarity and maintainability.
• By understanding how to effectively define and use numeric and string enumerations, you can more effectively manage sets of related values ​​in your TypeScript applications.
• Whether you choose numeric or string enums depends on your specific use case and the readability requirements of your code.