Example of React JSON data with fetch() function

import React, { Component } from 'react'

export class Subject extends Component {
    constructor(props){
       super(props);
       this.state={items:[],error: null,isLoaded: false};   

    }

    componentDidMount(){
          
      this.loadJSON(); 
    }

    loadJSON(){

       fetch("/android/menu_by_grade_json.php?grade=2")
      .then(res => res.json())
      .then(
        (result) => {
            console.log(result.subject);
          this.setState({
            isLoaded: true,
            items: result.subject            
          });
        },       
        (error) => {
          this.setState({
            isLoaded: true,
            error
          });
        }
      )
    }

   
    render() {
        return (
            <div>               

                <ul>
                {this.state.items.map(item => (
                    <li key={item.id}>
                    {item.name}
                    </li>
                ))}
                </ul>
            </div>
        )
    }
}

export default Subject 

render() {

     if(this.state.isLoaded){

        return (
            <div>     
                         
                 <ul>
                {this.state.subjects.map(item => (
                     <li key={item.id}>
                        
                        {item.id} {item.name}
                        <ul>
                           {   
                              item.chapter.map(chap=>{
                                  return <li key={chap.id}>{chap.name}</li>
                              })
                           }
                       </ul>
                    </li>                    
                ))}
                </ul>
            </div>
        )
        
       }else{

            return (
                <div>
                    Subjects not found
                </div>
            )

        }


    }