Usefall

Purpose

A complex thing exists.

I want to create a thing just like it, but with slight modifications.

Writer Tiger

I finished writing my first book yesterday!

class Protobook {
  constructor(introduction, chapter1, chapter2, conclusion) {
    this.introduction = introduction;
    this.chapter1 = chapter1;
    this.chapter2 = chapter2;
    this.conclusion = conclusion;
  }
}

tigersFirstBook = new Protobook(
  "There was once a great tiger.",
  "The tiger went on an adventure.",
  "He made lots of friends on his journey.",
  "The tiger fought a dragon and saved the world."
);

Writer Tiger

I want to make another version of the book that’s just like it,

But with a different ending.

Rewriting the book from scratch is hard to do!

Protobook

So in other words you want to use me as a prototype

to make more books?

Writer Tiger

Woah! You can talk!?

Yes, how can I do that?

Protobook

I am a special kind of book, a Protobook.

I can be used as a prototype,

because I have a clone() method.

Just call clone() and leave the rest to me!

class Protobook {
  constructor(introduction, chapter1, chapter2, conclusion) {
    this.introduction = introduction;
    this.chapter1 = chapter1;
    this.chapter2 = chapter2;
    this.conclusion = conclusion;
  }

  clone() {
    return new Protobook(
      this.introduction,
      this.chapter1,
      this.chapter2,
      this.conclusion
    );
  }
}

tigersFirstBook = new Protobook(
  "There was once a great tiger.",
  "The tiger went on an adventure.",
  "He made lots of friends on his journey.",
  "The tiger fought a dragon and saved the world."
);

let tigersSecondBook = tigersFirstBook.clone();
tigersSecondBook.conclusion = "The tiger befriended the dragon.";

Writer Tiger

That was easy! You are so cool Protobook!

You took care of all the cloning stuff!

Protobook

I know I am cool. Thank me more.

Solution

Use the complex thing as a prototype to create the other thing you wanted.

Other code can simply call the clone function of the prototype to create a copy and then make any further modifications.