Typescript - Object is possibly 'undefined' in interface

Question

In an Angular project, I am using an interface.

    export interface School {
      name: string = '';
      website: string;
      registrationNumber: string;
      dateEstablished: Date;
      address: string;
      country: [];
      companyLogo: any = '';
    
        clear() {
          this.name = '';
          this.website = '';
          this.registrationNumber = '';
          this.dateEstablished = null;
          this.address = '';
          this.country = [];
          this.companyLogo = '';
      }
    }

I got two errors:

Object is possibly 'undefined' - and all the "this." highlighted
Declaration or statement expected.ts(1128) - and the last closing curly brace highlighted.
expected call-signature: 'clear' to have a typedef (typedef)tslint(typedef)

How do I get these resolve?

Thanks

I could be mistaken, but I don't think an interface can contain a method implementation. Interfaces describe the members that should be present in the concrete implementation of the interface. They don't contain their definitions. Have you seen information that suggests otherwise? — JLRishe
– JLRishe, Commented Jun 6, 2021 at 19:32
@JLRishe - What's the best way to go about it. Kindly advise — user11352561
– user11352561, Commented Jun 6, 2021 at 19:38

thecOdemOnkey · Accepted Answer · 2021-06-06 20:11:34Z

1

You need an implementation of that interface like this:

file: school.ts

interface ISchool {
      name: string = '';
      website: string;
      registrationNumber: string;
      dateEstablished: Date;
      address: string;
      country: [];
      companyLogo: any = '';
    
      clear(): () => void; 

    }


export class School implements ISchool {

      // Declare all attributes here;
      public name: string = '';
      ...

      clear() {
          this.name = '';
          this.website = '';
          this.registrationNumber = '';
          this.dateEstablished = null;
          this.address = '';
          this.country = [];
          this.companyLogo = '';
      }

}

file app.ts

import {School} from 'school.ts';

const someSchool = new School();
someSchool.clear();

This is a basic object orientation technic so i would recommend to look up the use of classes together with interfaces.

You dont need the interface if you only have one type of school though.

edited Jun 6, 2021 at 20:11

answered Jun 6, 2021 at 19:46

thecOdemOnkey

2912 silver badges6 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

user11352561 Over a year ago

Which of the two (2) exports am I using? class or interface?

thecOdemOnkey Over a year ago

You have to instantiate an object of the class school like const someSchool = new School(); and then call someSchool.clear();

user11352561 Over a year ago

Sorry, I don't understand. Can you update the code?

Collectives™ on Stack Overflow

Typescript - Object is possibly 'undefined' in interface

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related