javascript classes

// @ts-check

class Title {
  #title;

  /**
   * @param {string} title
   */
  constructor(title) {
    if (typeof title != 'string') {
      throw new Error('input argument must be a string');
    }
    if (title.length > 80) {
      throw new Error('Title is too long');
    }
    this.#title = title;
  }

  get title() {
    return this.#title;
  }
}

class Content {
  #content;
  /** @param {string} content */
  constructor(content) {
    if (typeof content != 'string') {
      throw new Error('input argument must be a string');
    }
    this.#content = content;
  }

  get content() {
    return this.#content;
  }
}

class Url {
  #url;
  /** @param {string} url */
  constructor(url) {
    if (typeof url != 'string') {
      throw new Error('input argument must be a string');
    }
    if (!url.startsWith('http://') && !url.startsWith('https://')) {
      throw new Error('Invalid URL');
    }
    this.#url = url;
  }

  get url() {
    return this.#url;
  }
}


class Post {
  /**
   * @param {Title} title
   * @param {Content} content
   * @param {Url} imageUrl
   */
  constructor(title, content, imageUrl) {
    if (!(title instanceof Title)) {
      throw new Error('title must be an instance of Title');
    }
    if (!(content instanceof Content)) {
      throw new Error('content must be an instance of Content');
    }
    if (!(imageUrl instanceof Url)) {
      throw new Error('imageUrl must be an instance of Url');
    }
    this._title = title;
    this._content = content;
    this._imageUrl = imageUrl;
  }

  /** @returns {string} */
  get title() {
    return this._title.title;
  }

  /** @returns {string} */
  get content() {
    return this._content.content;
  }

  /** @returns {string} */
  get imageUrl() {
    return this._imageUrl.url;
  }

  toString() {
    return `${this.title}\n${this.content}\n${this.imageUrl}`;
  }
}

const post = new Post(
  new Title('This is a title.'),
  new Content('This is a post.'),
  new Url('http://example.com'));

console.log(post.toString());