Question

65

Javascript Conditional Inside TypeScript Interface

rated 0 times [ 72] [ 7] / answers: 1 / hits: 21251 / 7 Years ago, sat, may 27, 2017, 12:00:00

Is it possible to have a condition inside of an interface declaration in TypeScript. What I'm looking for is a way to say, based on the value of the first key, the second key can be these values.

Example (non functioning):

interface getSublistValue {



    /** The internal ID of the sublist. */

    sublistId: 'item' | 'partners';



    /** The internal ID of a sublist field. */

    if (this.sublistId === 'item') {

        fieldId: 'itemname' | 'quantity';

    }



    if (this.sublistId === 'partners') {

        fieldId: 'partnername' | 'location';

    }

}

Answers

Only authorized users can answer the question. Please sign in first, or register a free account.

sabrina

Add To Favorites

Follow

Total Points: 92

Total Questions: 92

Total Answers: 85

Location: Palestine

Member since Thu, Feb 2, 2023

1 Year ago

answered 7 Years ago ellisw · Accepted Answer

No there's not. The best thing to do is to create separate interfaces that describe the two different types of data.

For example:

interface SublistItem {

    sublistId: 'item';

    fieldId: 'itemname' | 'quantity';

}



interface SublistPartners {

    sublistId: 'partners';

    fieldId: 'partnername' | 'location';

}



function getData(): SublistItem | SublistPartners {

    return (Math.random() < 0.5)

        ? { sublistId: 'item', fieldId: 'itemname' }

        : { sublistId: 'partners', fieldId: 'partnername' };

}



const someValue = getData();



if (someValue.sublistId === item) {

    // SublistItem in here

}

else {

    // SublistPartners in here

}