react

class App extends React.Component { //定义组件，继承父类
  constructor() {//constructor 是和 class 一起用来创建和初始化对象的特殊方法。
    super()//在装载组件(mounting)之前调用会React组件的构造函数。当实现React.Component子类的构造函数时，应该在任何其他语句之前调用super(props)
    this.state = {//设置初始状态
      todos: []
    }
  }
  // 绑定键盘回车事件，添加新任务
  handlerKeyUp(e) {
    if(e.keyCode == 13) {
      let value = e.target.value;
      if(!value) return false;
      let newTodoItem = {
        text: value,
        isDone: false
      };
      e.target.value = '';
      this.state.todos.push(newTodoItem)
      this.setState({todos: this.state.todos});  //修改状态值，每次修改以后，自动调用 this.render 方法，再次渲染组件。
    }
  }
  render(){
    return (
      

        
        

          {this.state.todos.map((todo,index) => {{
            return (
                
{todo.text}
//Keys help React identify which items have changed, are added, or are removed. Keys should be given to the elements inside the array to give the elements a stable identity
            )
          }})}
        
      
    )
  }
}
ReactDOM.render(,document.getElementById('app'))