State

State is similar to props, but it is private and fully controlled by the component.
link - channel9.msdn.com/Shows/Web-Wednesday/How-do-I-work-with-state-in-React

interface IState_BETClass { 
  sItems: IListItem[] 
} 

States should only be used attributes that need to change
A parent can pass in props to set the default values for the state during construction.

State is a feature only available in classes.

  constructor(props) { 
    super(props); 
    this.state = {date: new Date()}; 
  }