React state with calculated fields

Question

I have a react component, which has properties and state. Some fields of state contain input data (uplifted from input control), but there is also fields in the state that must

Answer 1

You can save calculated result in this.calculated instead of this.state. It is dependent data. All data which causes update and render is already in state and props.

class Component extends React.Component {
  constructor(props) {
    super(props)
    state = {
      b: 0
    }
  }

  updateThis = (event) => {
    this.setState({ b: event.target.value });
  }

  componentWillUpdate(nextProps,nextState){
    this.calculated.field1=f(nextProps.a, nextState.b)
  }

  render() {
    return (
      

        A =  

        B =  

        f(A,B) = {this.calculated.field1} 

      
    );
  }
}

class ParentComponent extends React.Component {
  constructor(props) {
    super(props)
    state = {
      a: 0
    }
  }

  render() {
     return (
       this.setState({a: event.target.value})}
         a={this.state.a}
       />
     }
  }
}