2-lit-element/solutions/9-read-unread-counter.html

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">

  <script type="module">
    import {LitElement, html, css} from 'https://unpkg.com/lit-element@2.0.0-rc.5?module';
    import 'https://unpkg.com/@polymer/paper-button/paper-button.js?module';

    function filterStories(stories, filter){
      return stories.filter((article) => {
        if (filter === 'read') return article.read;
        if (filter === 'unread') return !article.read;
        if (filter === 'all') return true;
      });
    }

    class MyElement extends LitElement {
      static get styles() {
        return css`
          :host {
            display: block;
          }
        `;
      }

      static get properties() {
        return {
          articles: { type: Array },
          filter: { type: String }
        };
      }

      constructor() {
        super();
        this.articles = [];
        // add a filter
        this.filter = 'all';
      }

      connectedCallback() {
        super.connectedCallback();
        fetch('https://newsapi.org/v2/everything?q=tech&apiKey=<your-api-key>')
          .then(response => response.json())
          .then(response => {
            this.articles = response.articles.map((article, i) => ({...article, id: i, read: false}));
          })
      }

      _toggleReadStatus(e) {
        this.articles[e.detail].read = !this.articles[e.detail].read;
        this.requestUpdate();
      }

      render() {
        const filteredArticles = filterStories(this.stories, this.filter);

        return html`
          <paper-button raised @click=${() => this.filter = 'all'}>
            all
          </paper-button>

          <paper-button raised @click=${() => this.filter = 'read'}>
            read (${filterStories('read').length})
          </paper-button>

          <paper-button raised @click=${() => this.filter = 'unread'}>
            unread (${filterStories('unread').length})
          </paper-button>

          <ul>
            <!-- apply filter to the array -->
            ${filteredArticles.map(article => html`
              <my-article
                .title=${article.title}
                .description=${article.description}
                .read=${article.read}
                .id=${article.id}
                @toggled=${this._toggleReadStatus}
              ></my-article>
            `)}
          </ul>
        `;
      }
    }

    customElements.define('my-element', MyElement);

    class MyArticle extends LitElement {
      static get styles() {
        return css`
          :host {
            display: block;
          }
        `;
      }

      static get properties() {
        return {
          title: { type: String },
          description: { type: String },
          read: { type: Boolean },
          id: { type: Number }
        }
      }

      // dispatch an event to the parent element
      _toggleRead() {
        this.dispatchEvent(new CustomEvent('toggled', { detail: this.id }));
      }

      render() {
        return html`
          <li>
            <paper-button @click=${this._toggleRead}>
              ${this.read ? 'read' : 'unread'}
            </paper-button>

            <h2>${this.title}</h2>
            <p>${this.description}</p>
          </li>
        `;
      }
    }
    customElements.define('my-article', MyArticle);
  </script>
</head>

<body>
  <my-element></my-element>
</body>
</html>