CODEWITHSUNDEEP
typescripttypescript-generics
btx
btx

Reputation: 2497

Return type based on input type

I know there are similar questions, but I don't get it.

How can I configure the types to have inputType = outputType ?

public addReadableTime(message: PublicMsg | PrivateMsg): PublicMsg | PrivateMsg {
   message.displayTime = moment(message.lastModified).format('HH:mm');
   return message;
}

// ...

const publicMsg = this.addReadableTime(publicMsg);

TS2322: Type 'PublicMsg | PrivateMsg' is not assignable to type 'PublicMsg'.   Property 'publicChannelMessageId' is missing in type 'PrivateMsg' but required in type 'PublicMsg'.

Upvotes: 0

Views: 38

Answers (1)

JLRishe
JLRishe

Reputation: 101758

Seems like what you need is a generic method with a type constraint:

public addReadableTime<T extends PublicMsg | PrivateMsg>(message: T): T {
   message.displayTime = moment(message.lastModified).format('HH:mm');
   return message;
}

// ...
const publicMsg2 = this.addReadableTime(publicMsg);

Upvotes: 2

Related Questions