소스 그대로 복붙하면 Unexpected token, expected "," (14:6) 오류가 납니다.

constructor (props){
  super(props);
  this.state = {
    subject : { title : 'WEB' , sub : 'World Wide Web!' },
    contents : [
      {id : 1 , title : 'HTML' , desc : 'HTML is for information'},
      {id : 2 , title : 'CSS' , desc : 'CSS is for design'},
      {id : 3 , title : 'JavaScript' , desc : 'JavaScript is for interactive'},
    ]
  }
}

subject 뒤에 쉼표 추가해주시면 됩니다.