React rerender

by evgkch

HTML

<div id="app"></div>

CSS

body {
  background: #20262E;
  padding: 20px;
  font-family: Helvetica;
}

#app {
  background: #fff;
  border-radius: 4px;
  padding: 20px;
  transition: all 0.2s;
}

li {
  margin: 8px 0;
}

h2 {
  font-weight: bold;
  margin-bottom: 15px;
}

.done {
  color: rgba(0, 0, 0, 0.3);
  text-decoration: line-through;
}

input {
  margin-right: 5px;
}

React

// If Item instance of Component - we have rerender
// If Item instance of PureComponent - it's ok
class Item extends React.PureComponent {
	render(){
  	console.log('render')
  	return (
    	<li>
        <label>
          <input type="checkbox" checked={this.props.item.done} onChange={() => this.props.onChange(this.props.index)}/> 
          <span className={this.props.item.done ? "done" : ""}>{this.props.item.text}</span>
        </label>
      </li>
    );
  }
}

class TodoApp extends React.Component {
  constructor(props) {
    super(props)
    this.state = {
    	items: [
      	{ text: "Learn JavaScript", done: false },
        { text: "Learn React", done: false },
        { text: "Play around in JSFiddle", done: true },
        { text: "Build something awesome", done: true }
      ],
      flag: 0
    }
  }
  
  onChange = index=> {
  	this.setState({ items: this.state.items.map((item, i) => {
    	if (index == i)
      	return {
        	done: item.done,
          text: item.text + '*',
        };
      else
      	return item;
    }) })
  }
  
  renderItem = (item, index)=>{
  	return (
      <Item item={item} key={index} index={index} onChange={this.onChange} />
    );
  }
   
  render() {
    return (
      <div>
        <h2>Todos:</h2>
        <ol>
        {this.state.items.map(this.renderItem)}
        </ol>
      </div>
    )
  }
}

ReactDOM.render(<TodoApp />, document.querySelector("#app"))