what is use of enum in typescript. If it's purpose is only to make code redable can't we just use constant for same purpose
enum Color { Red = 1, Green = 2, Blue = 4 }; let obj1: Color = Color.Red; obj1 = 100; // does not show any error in IDE while enum should accept some specific values If there is no advantage of typechecking, Can't it be just written as.
const BasicColor = { Red: 1, Green: 2, Blue: 4 }; let obj2 = BasicColor.Red; First, in the following:
const BasicColor = { Red: 1, Green: 2, Blue: 4 }; Red, Green, and Blue are still mutable (whereas they are not in an enum).
Enums also provide a few things:
To get that with something like a namespace, for example, you have to do something like
export namespace Color export const Red = 1 export type Red = typeof Red; export const Green = 2; export type Green = 2; export const Blue = 3; export type Blue = typeof Blue; } export type Color = Color.Red | Color.Blue | Color.Green What you're also noting is some unfortunate legacy behavior where TypeScript permits assignment from any numeric value to a numeric enum.
But if you're using a string enum, you won't get that behavior. There are also other things like exhaustiveness checking that you can enable with union enums:
enum E { Hello = "hello", Beautiful = "beautiful", World = "world" } // if a type has not been exhaustively tested, // TypeScript will issue an error when passing // that value into this function function assertNever(x: never) { throw new Error("Unexpected value " + x); } declare var x: E; switch (x) { case E.Hello: case E.Beautiful: case E.World: // do stuff... break; default: assertNever(x); }