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HTML

              
                <div id="root"></div>
              
            
!

CSS

              
                @use postcss-cssnext;
@use postcss-simple-vars;
@use postcss-custom-media;
@use postcss-nested;
@use postcss-mixins;
@use lost;

body {
    background-color: #333;
    font-family: "Roboto";
}

main {
    max-width: 100vw;
    width: 100%;
    height: 100vh;
    display: flex;
    flex: 1;
    flex-flow: column nowrap;
    align-items: center;
    justify-content: center;
}

button {
    background-color: #666;
    border-radius: 5px;
    color: white;
    border: 0;
    padding: 20px;
    bottom: 50%;
    font-weight: bold;
    cursor: pointer;
    text-transform: uppercase;
    transition: 0.25s all;
    max-width: 200px;
    width: 100%;
    
    &:hover {
        background-color: #F07818;
    }
}

ol {
    list-style-type: none;
    display: flex;
    flex-flow: row;
    width: 100%;
    max-width: 500px;
    padding: 0;
    justify-content: space-around;
    align-items: center;
    margin: 0 0 20px;
    
    & li {
        flex: 0 0 auto;
    }
}

.bulb {
    background-color: #888;
    border-radius: 50%;
    min-width: 20px;
    min-height: 20px;
    padding: 10px;
    display: block;
    text-align: center;
    box-shadow: 0 2px 0 0 rgba(0, 0, 0, 0.5);
    position: relative;
    
    &.pure:before {
        content: 'P';
        font-weight: bold;
        color: white;
    }
    
    &:after {
        position: absolute;
        width: 100%;
        background-color: #D36112;
        height: 5px;
        content: '';
        z-index: -1;
        top: 50%;
        left: 50%;
        transform: translate(5px, -50%);
    }
    
    &:last-child:after {
        content: none;
    }
    
    &.on {
        background-color: #FCEBB6;
        box-shadow: 0 0 3px 6px rgba(230,219,151, 0.4);
    }
}
              
            
!

JS

              
                // Create new LightContext. LightContext will return a Provider and Consumer
const LightContext = React.createContext('areLightsOn');
class LightProvider extends React.Component {
    render(){
        // Allow Provider to set 'value' as whatever 'areLightsOn' prop is passed in
        return (
            <LightContext.Provider value={ this.props.areLightsOn } >
                { this.props.children }
            </LightContext.Provider>
        )
    }
}


// 'areLightsOn' are passed in as a prop
const Bulb = ({ children, className, areLightsOn })=> {
    const lightStateClassName = areLightsOn ? 'on' : 'off';
    const classNames = `bulb ${className} ${lightStateClassName}`;
    return (
        <li className={classNames}>{children}</li>
    );
}

// Add a 'Consumer' to take current 'areLightsOn' state
class LightBulb extends React.Component {
    render(){
        return (
            <LightContext.Consumer>
                { areLightsOn => (
                    <Bulb {...this.props} areLightsOn={areLightsOn} /> 
                )}
            </LightContext.Consumer>
        );
    }  
};

// Add a 'Consumer' to take current 'areLightsOn' state
class PureLightBulb extends React.PureComponent {
    render(){
        return (
            <LightContext.Consumer>
                { areLightsOn => (
                    <Bulb className="pure" {...this.props} areLightsOn={areLightsOn} /> 
                )}
            </LightContext.Consumer>
        );
    }  
}

class Wire extends React.Component {
    render(){
        return (
            <ol>
                <LightBulb />
                <PureLightBulb />
                <LightBulb />
                <LightBulb />
                <LightBulb />
                <PureLightBulb />
                <PureLightBulb />
                <PureLightBulb />
            </ol>
        )
    }
}

class Lights extends React.PureComponent {
    constructor(props){
        super(props);
        
        this.state = {
            areLightsOn: false   
        };
        
        this.toggleLights = this.toggleLights.bind(this);
    }
    
    // Remove 'getChildContext', no longer need with new context
    
    toggleLights(){
        this.setState({
           areLightsOn: ! this.state.areLightsOn 
        });
    }
    
    render(){
        return (             
            <main>
                {/* Wrap Wire in new LightProvider. Pass in state to be utilized by context */}
                <LightProvider areLightsOn={ this.state.areLightsOn }>
                    <Wire />
                </LightProvider>
                {/* Update this provider to be the opposite */}                
                <LightProvider areLightsOn={ ! this.state.areLightsOn }>
                    <Wire />
                </LightProvider>

                <button type="button" onClick={this.toggleLights}>
                    Toggle Lights
                </button>
            </main>            
        );
    }
}

// Remove 'childContextTypes', no longer need with new context

ReactDOM.render(<Lights />, document.getElementById('root'));
              
            
!
999px

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