ChildComponentReactControl

import * as React from 'react';
import { ChildComponentState } from './ChildComponentState';

import { WebPartContext } from '@microsoft/sp-webpart-base';
export interface ChildComponentProps
{ 
    context : WebPartContext;
    childoutput?: (item: any) => void;
}

export default class ChildComponent extends React.Component<ChildComponentProps, ChildComponentState> {

  constructor()
  {
      super();
      this.state = {
          stateprop1  : "",
          stateprop2  : this.props.prop1
      };   
  }

  public componentWillMount()
  {
  ...
  }
  
   /**
   * Any event method to set the value
   * @param item 
   */
  private _onItemChange = (item: any) => {
   const { childoutput } = this.props;
   if (childoutput) {
            childoutput(item);
   }
  }
  
  public render(): React.ReactElement<ChildComponentProps> {
    return (
    <div> .. </div>
    )};
}