saving-the-react-novice-good-example.jsx

class SomeProblematicComponent extends React.Component {
  constructor(props) {
    super(props)
    this.state = {
      data = [...props.data]
    }
  }
  onChange = (arg) => {
    this.setState(prev => {
      const data = [...prev.data]
      return {data: data.map(itm => {...itm, a:arg})}
    }
  }
  render() {
    // it would call onChange somewhere
  }
}