Example of using setInterval function in React

import React, { Component } from 'react';
import { Radio, Button, Icon } from 'antd';

class List extends Component {
  constructor(props) {
    super(props);
    this.state = {
      online: false,
    };
  };

  handleLogin=()=>{
    localStorage.setItem('username','xuzheng');
  };

  handleLogout=()=>{
    localStorage.removeItem('username');
  };

  componentDidMount(){
    this.timer = setInterval(() => {
      this.setState({
        online: localStorage.username ? true : false,
      })
    }, 1000);
  }

  componentWillUnmount() {
    if (this.timer != null) {
      clearInterval(this.timer);
    }
  }

  render() {
    return (
      <div>
        <div>
          <Icon type='user' style={{marginRight:'8px'}}/>
          <span>{localStorage.username ? localStorage.username : 'Not logged in'}</span>
        </div>
        <div style={{marginTop:'20px'}}>
          <Button type='primary' onClick={this.handleLogin}>Login</Button>
        </div>
        <div style={{marginTop:'20px'}}>
          <Button type='primary' onClick={this.handleLogout}>Logout</Button>
        </div>
      </div>
    )
  }
}

export default List;