React

by Trina Lu

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

class CompareForm extends React.Component {
	state = {
  	initPerson: {
    	name: '',
      age: 0,
      food: []

    },
  	person: {
			name: '',
      age: 0,
      food: []
    }
  }

	static getDerivedStateFromProps(nextProps, prevState) {
  	console.log('getDerivedStateFromProps')
    if (nextProps.initPerson !== prevState.initPerson) {
    	console.log('its new!', nextProps.initPerson, prevState.initPerson)
      return {
      	initPerson: { ...nextProps.initPerson },
        person: nextProps.initPerson
      };
    }
    return null;
  }
  
  updateName = () => {
  	this.setState(state => {
    	return {
      	person: {
        	...state.person,
          name: 'Usagit'
        }
      }
    })
  }
  
  render() {
  	return (
    	<pre>
        <button onClick={this.updateName}>Usagi!</button>
    	  <code>{JSON.stringify(this.props, null, 4)}</code>
    	  <code>{JSON.stringify(this.state, null, 4)}</code>
    	</pre>
    )
  }
}

class App extends React.Component {
	state = {
  	name: 'Trina',
    age: 12,
    food: ['noodles', 'mos']
  }
  
  trina = {
  	name: 'Trina',
    age: 12,
    food: ['noodles', 'mos']
  }
  
  updateState = () => {
  	this.setState(state => {
    	return {
      	name: 'Sherry',
        age: 25,
        food: ['choco']
      }
    })
    
    this.trina.name = 'Pisuke';
  }
  
	render() {
  	return (
    	<div>
        <button onClick={this.updateState}>updateState</button>
    	  <CompareForm initPerson={this.trina} />
    	</div>
		) 
  }
}

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