Typescript enums typing error (argument of type 'string' is not assignable to parameter of type)

Question

I have an enum define as follows:

export enum taskTypes {
  WORK = 'work',
  SLEEP = 'sleep',
  EXERCISE = 'exercise',
  EAT = 'eat'
}

On the top of my class I define the currentTask as follows:

private currentTask: string;

However, when I use the enums in [WORK, SLEEP].includes(currentTask) I get the following error.

Argument of type 'string' is not assignable to parameter of type 'currentTask'

The weird thing is when I simply just change it to use the actual string it doesn't complain.

['work', 'sleep'].includes(currentTask) ===> this works.

So what am I missing here?

Klas Mellbourn · Accepted Answer · 2019-10-21 22:23:17Z

8

currentTask is of type string, but WORK and SLEEP is enum members of type taskTypes

So [WORK, SLEEP] is an array of taskTypes enums. Such an array can never contain a string.

['work', 'sleep'] is an array of strings, which can contain a string.

If you type the private memeber to be of type taskTypes it will also work

private currentTask: taskTypes

answered Oct 21, 2019 at 22:23

Klas Mellbourn

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2 Comments

lion_bash Over a year ago

Ah, I see, one question though, type taskTypes is an enum which is type string right?

Klas Mellbourn Over a year ago

@honeybadger_execute no, enums and strings are different types in TypeScript. "String enums" are a special case of enums, that "serialize" well (e.g. log), but still not the same as strings. typescriptlang.org/docs/handbook/enums.html

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