front__codeschool-react/src/comments.js

/*
Good practices:
- name CSS classNamees like the associated component
- prefix non-React method names by an "_"
- pass a "key" attribute to elements in a loop

State
- direct reads, write through setState()
- declare initial state in constructor()
- setState() calls render(): beware loops = avoid it in render()

Refs:
- are called by React during render()
- (foo) => { this._bar = foo; ) translates to function(foo) { this._bar = foo; }.bind(this);

Events:
- React events are "synthetic" events, masking the browser behaviour differences
- https://facebook.github.io/react/docs/events.html

Lifecycle methods:
- Main: componentWillMount / componentDidMount / componentWillUnmount
- fetch initial data from cWM, start a refresh poll loop from cDM, stop loop from cWU
 - https://facebook.github.io/react/docs/react-component.html

JSX:
- "className", not "class"
- knows how to render an array of JSX elements, not just one.
 */

class Comment extends React.Component {
  render() {
    return (
      <div className="comment">
        <p className="comment-header">{this.props.author}</p>
        <p className="comment-body">
          {this.props.body}
        </p>
        <div className="comment-footer">
          <a href="#" className="comment-footer-delete">
            Delete comment
          </a>
        </div>
      </div>
    );
  }
}

class CommentForm extends React.Component {
  _handleSubmit(event) {
    // Prevent the page from reloading.
    event.preventDefault();
    // this._author/this._body are populated by refs in JSX
    let author = this._author;
    let body = this._body;
    // Since they are elements, we need to take their ".value".
    this.props.addComment(author.value, body.value);
    // addComment is called on this.props, meaning it is passed by component parent.
  }

  render() {
    return (
      <form className="comment-form" onSubmit={this._handleSubmit.bind(this)}>
        <label>Join the discussion</label>
        <div className="comment-form-fields">
          <input placeholder="Name:"
            ref={(input) => { this._author = input; } } /* "this" is CommentForm... *//>
          <textarea placeholder="Comment:"
            ref={(textarea) => { this._body = textarea; /* ...because of lexical scope */ } } />
        </div>
        <div className="comment-form-actions">
          <button type="submit">Post comment</button>
        </div>
      </form>
    );
  }
}

class CommentBox extends React.Component {
  constructor() {
    super();
    this.state = {
      showComments: false,
      comments: []
    };
  }

  _addComment(author, body) {
    const comment = {
      id: this.state.comments.length + 1,
      author,
      body
    };
    // concat(), not push(): push() mutates the data, concat doesn't.
    // By allocating a new reference, for comments, React detects the change fast.
    this.setState({comments: this.state.comments.concat([comment])});
  }

  _fetchComments() {
    jQuery.ajax({
      method: "GET",
      url: "/static/comments.json",
      // Arrow function: keep "this" binding to the class instance.
      success: (comments) => {
        this.setState({comments});
      }
    });
  }

  _getComments() {
    return this.state.comments.map((comment) => {
      return (<Comment
        author={comment.author}
        body={comment.body}
        key={comment.id} />);
    });
  }

  _getCommentsTitle(commentCount) {
    if (commentCount === 0) {
      return "No comments yet";
    } else if (commentCount === 1) {
      return "1 comment";
    }

    return `${commentCount} comments`;
  }

  _handleClick() {
    this.setState({
      showComments: !this.state.showComments
    });
  }

  componentDidMount() {
    this._timer = setInterval(() => this._fetchComments(), 5000);
  }

  componentWillMount() {
    this._fetchComments();
  }

  componentWillUnmount() {
    clearInterval(this._timer);
  }

  render() {
    const comments = this._getComments();
    let buttonText = "Show comments";
    let commentNodes;
    if (this.state.showComments) {
      commentNodes = <div className="comment-list">{comments}</div>;
      buttonText = "Hide comments";
    }
    return (
      <div className="comment-box">
        <button onClick={this._handleClick.bind(this)}>{buttonText}</button>
        <h4 className="comment-count">{this._getCommentsTitle(comments.length)}</h4>
        <CommentForm addComment={this._addComment.bind(this)} />
        {commentNodes}
      </div>
    );
  }
}

ReactDOM.render(
  <CommentBox />, document.getElementById('comments-app')
);