A simple example demonstrating shared behaivor using abstract base class and interface in Typescript

abstract_summary.ts

abstract class Summarize {
  abstract summarize(): string;
  
}

class NewsArticle extends Summarize {
  headline: string;
  place: string;
  author: string;
  content: string;

  constructor( headline: string, place: string, author: string, content: string){
    super();
    this.headline = headline;
    this.place = place;
    this.author = author;
    this.content = content;      
      
  }

  summarize(): string{
    return  `${this.headline}, by ${this.author} (${this.place})` 
  }
}


class Tweet extends Summarize {
  username: string;
  content: string;
  reply: boolean;
  retweet: boolean;

  constructor( username: string, content: string, reply: boolean, retweet: boolean){
    super();
    this.username = username;
    this.content = content;
    this.reply = reply;
    this.retweet = retweet;      
  }

   summarize() :string {
      return `${this.username}: ${this.content}`
    }


}

client.ts

function main(): void {
  const news = new NewsArticle("The AI invasion has begun.",
                              "Abuja", 
                              "John Doe", 
                              "The AI invasion began with the release of a transformer.")
  
  const tweet = new Tweet("John Doe", "Read my latest news article.", false, false);

  console.log(`Today's news: ${news.summarize()}`);
  console.log(`1 new tweet: ${tweet.summarize()}`);

}

main()
/* Output:
Today's news: The AI invasion has begun., by John Doe (Abuja)
1 new tweet: John Doe: Read my latest news article.
*/

interface_summary.ts

interface Summarize {
  summarize(): string;  
}

class NewsArticle implements Summarize {
  headline: string;
  place: string;
  author: string;
  content: string;

  constructor( headline: string, place: string, author: string, content: string){
    this.headline = headline;
    this.place = place;
    this.author = author;
    this.content = content;
  }

  summarize(): string{
    return  `${this.headline}, by ${this.author} (${this.place})` 
  }
}


class Tweet implements Summarize {
  username: string;
  content: string;
  reply: boolean;
  retweet: boolean;

  constructor( username: string, content: string, reply: boolean, retweet: boolean){
    this.username = username;
    this.content = content;
    this.reply = reply;
    this.retweet = retweet;      
  }

   summarize() :string {
      return `${this.username}: ${this.content}`
    }
}