React

HTML

<script src="https://unpkg.com/react@16.12.0/umd/react.production.min.js"></script>
<script src="https://unpkg.com/react-dom@16.12.0/umd/react-dom.production.min.js"></script>
<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;
}

Babel + JSX

function bigArray() {
  console.log("new array");
	return new ArrayBuffer(10 * 1000 * 1000);
}

class Item extends React.Component {
  
  componentWillUnmount() {
  	console.log("unmount");
  }
  
  render() {
    return (
      <li>
        <label>
          <input type="checkbox" disabled readOnly checked={this.props.done} /> 
          <span className={this.props.done ? "done" : ""}>{this.props.text}</span>
        </label>
      </li>
    );
  }
}

class TodoApp extends React.Component {
  constructor(props) {
    super(props)
    this.state = {
    	items: [
      	{ id: 1, text: "Learn JavaScript", done: true, buffer: bigArray() },
        { id: 2, text: "Learn React", done: true, buffer: bigArray() },
      ]
    }
  }
  
  onRefresh() {
  	this.setState({
    	items: [
        { id: 3, text: "Check chrome dev tools memory tab - and see more than one JSArrayBufferData (only one should exist)", done: false, buffer: bigArray() }
      ]
    });
  }
  
  
  render() {
    return (
      <div>
        <h2>Todos:</h2>
        <ol>
        {this.state.items.map(item => <Item key={item.id} text={item.text} done={item.done}/>)}
        </ol>
        Press this button: <button onClick={() => this.onRefresh()}>Refresh</button>
      </div>
    )
  }
}

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