CODEWITHSUNDEEP
typescriptgenerics
Jem
Jem

Reputation: 6406

Typescript: Typed interface doesn't allow a value from its type string litteral

I've created a scale down version of my problem.

The class must initialize the default value of its "status" property. It's of type T which extends the string litteral type "PossibleStatus" made of 3 possible strings.

Typescript doesn't accept this. Can you help me figure out why?

A stackblitz to see it live

export type PossibleStatuses = 'idle' | 'on' | 'off';

export class StatefulNode<T extends PossibleStatuses> {

  private status: T = 'idle';

  constructor() { }

}

Upvotes: 0

Views: 38

Answers (1)

basarat
basarat

Reputation: 276199

The following code demonstrates why you cannot initiate the status (type X = 'on' extends PossibleStatuses but doesn't include 'idle'): 

export type PossibleStatuses = 'idle' | 'on' | 'off';

export class StatefulNode<T extends PossibleStatuses> {
  // Error
  private status: T = 'idle';
}

// Because
const unsafe = new StatefulNode<'on'>();

Upvotes: 1

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