CurrentTimeRenderCb.js

import {render} from 'react-dom';
import React, {Component, Children, cloneElement} from 'react';

class CurrentTime extends Component {
    state = {time: ''};
    componentDidMount() {
        this._interval = setInterval(() => this.setState({time: this.getTime()}), 50);
    }
    componentWillUnmount() {
        clearInterval(this._interval);
    }
    getTime(){
        let t = new Date();
        return `${t.getHours()}:${t.getMinutes()}:${t.getSeconds()}`;
    }
    render() {
        let {children: renderFn} = this.props;
        return renderFn({time: this.state.time});
    }
}

render(
    <div>
        <CurrentTime>
            {({time}) => (
                <div>
                    <span style={{color: 'orange'}}>Time is {time}</span>
                </div>
            )}
        </CurrentTime>
    </div>, document.getElementById('home')
);