Best way to cast an object to a TypeScript Enum Value-CodePudding

Is there an easy/best practice way to cast an any value to a TypeScript Enum and throw an exception if there is no value.

As an example

You have an express request object and are using the query.option value. Your application knows it only has two valid states a|b. However, the reality of the internet and request object is that it can be many things (undefined, a, b, foo).

enum OPTIONS_ENUM {
  a = 'a',
  b = 'b'
}

function handleRequest(req: Request): OPTIONS_ENUM {
  // This will error because query.option is an any
  return OPTIONS_ENUM[req.query?.option]
}

What I have been doing seems a little verbose. I have a "cast" function next to each enum that will throw if the ENUM does not have a value.

function castToOptionsEnum(option: any): OPTIONS_ENUM {
  if (!Object.values(OPTIONS_ENUM)?.includes(option)) {
    throw new Error(`Invalid Value for option, must be one of ${Object.values(OPTIONS_ENUM)}`)
  }
 
  // @ts-ignore
  return OPTIONS_ENUM[option]
}

function handleRequest(req: Request) {
  // This will error because the option query is unknowable 
  return castToOptionsEnum(req.query?.option)
}

CodePudding user response：

you can "simply" cast option to OPTIONS_ENUM when accessing OPTIONS_ENUM in castToOptionsEnum:

function castToOptionsEnum(option: any): OPTIONS_ENUM {
    if (!Object.values(OPTIONS_ENUM)?.includes(option)) {
        throw new Error(`Invalid Value for option, must be one of ${Object.values(OPTIONS_ENUM)}`);
    }

    return OPTIONS_ENUM[option as OPTIONS_ENUM];
}

This will remove any compile errors (I would suggest to remove // @ts-ignore aswell, since it "hides" compile errors - but that's up to you ^^).