Component life cycle methods

There are a couple of tricks I want to show you before we wrap up. The first is a life cycle method we can use to tell when a component's properties will change. We can use this to change the appearance of a component, or refresh the internal state.

We can add this method to PageEditor, for example:

class PageEditor extends Component {
    constructor(props) {
        super(props);

        this.state = {
            "changed": false
        };

        this.bind(
            "onCancel",
            "onUpdate"
        );
    }

    isChanged(next, previous) {
        return JSON.stringify(next) !== JSON.stringify(previous)
    }

    componentWillReceiveProps(props) {
        this.setState({
            "changed": this.isChanged(props, this.props)
        });
    }

    render() {
        return <div>
            <input
                type="text"
                name="title"
          ...