Using Class.prototype.state for default initial state.

protostate.jsx

class App extends React.Component {
  
  startWondering = (e) => {
    this.setState({ feeling: 'wondering' })
  }
  
  render() {
    const { feeling } = this.state
    const { feeling: initialFeeling } = this.__proto__.state
    
    if (feeling != initialFeeling) {
      return <p>I am now { feeling }. Usually I am { initialFeeling }.</p>
    } else {
      return <p onClick={ this.startWondering }>I think I am always { feeling }.</p>
    }
  }
}

// Are we missing an idiomatic way to do this inside the class definition? 
App.prototype.state = { feeling: "fine with it" }

React.render(<App />, document.getElementById('app'))