How to update multiple child states in React Class Components independently?

Question

I know how it can be done with Functional Components. But when it comes to class components, I'm having few questions to be clarified.

I've a class here,

class MyTable extends Component {
   constructor(props) {
      super(props);
       this.state = {
          page:0,
          rowsPerPage:10
       }
   }

   handleChangePage(event) {
      //Here I want to update only **page** keeping **rowsPerPage** intact
   }

   handleChangeRowsPerPage(event) {
      //Here I want to update only **rowsPerPage** keeping **page** intact
   }

   render() {
      return(
         <SomeComponent
           onChangePage={this.handleChangePage}
           onChangeRowsPerPage={this.handleChangeRowsPerPage}
         />
      )
   }
}
export default Mytable;

So here what I want to know is,

1. If I want to update only page inside the state object, should I have to preserve rowsPerPage and update them both as this.setState({page:<updatedValue>, rowsPerPage:<preservedValue>); And Vice versa

2. What code goes inside handleChangePage and handleChangeRowsPerPage, if we can update independent properties inside a state object.

3. What's the best practice when we've several such states and we want to update each one independently?

Answer 1

You can update page and rowsPerPage independently as I did bellow. You have just to call this.setState and passing and object with the key of state you want to update

class MyTable extends React.Component {
   constructor(props) {
      super(props);
       this.state = {
          page:0,
          rowsPerPage:10
       }
       
       this.handleChangePage = this.handleChangePage.bind(this);
       this.handleChangeRowsPerPage = this.handleChangeRowsPerPage.bind(this);
   }

   handleChangePage(event) {
      //Here I want to update only **page** keeping **rowsPerPage** intact
      this.setState({page: event.target.value});
   }

   handleChangeRowsPerPage(event) {
      //Here I want to update only **rowsPerPage** keeping **page** intact
      this.setState({rowsPerPage: event.target.value});
   }

   render() {
      return (
         <div>
            <div>
              Page <input type="text" value={this.state.page} onChange={this.handleChangePage} />
            </div>
            
            <div>
              rowsPerPage <input type="text" value={this.state.rowsPerPage} onChange={this.handleChangeRowsPerPage} /></div>
         </div>
      )
   }
}

ReactDOM.render(<MyTable />, document.getElementById('root'));

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>
<div id="root"></div>