use to use a function in child element when sending value to props in parent code example

Example: pass data from child component to parent component react native

class Parent extends React.Component {
  state = { message: "" }
  callbackFunction = (childData) => {
        this.setState({message: childData})
  },
  render() {
          return (
              <div>
                   <Child1 parentCallback = {this.callbackFunction}/>
                   <p> {this.state.message} </p>
              </div>
          );
  }
}

class Child1 extends React.Component{
  sendData = () => {
           this.props.parentCallback("Hey Popsie, How’s it going?");
      },
  render() { 
  //you can call function sendData whenever you'd like to send data from child component to Parent component.
      }
};