title: Property 'state' does not exist on type 'FetchPeriod'
body: <p>I'm trying to learn ReactJS following this tutorial:
  <a href="https://dzone.com/articles/aspnet-core-crud-with-reactjs-and-entity-framework" rel="noreferrer">Tutorial</a></p>
  
  <p>I'm new to the programming language so i'm clueless as to what to do now.</p>
  
  <p>When I try to add the "Fetchemployee.tsx" file, I get an error at the <code>this.state</code> method.</p>
  
  <blockquote>
    <p>(TS) Property 'state' does not exist on type 'FetchPeriod'</p>
  </blockquote>
  
  <p>This is the code:</p>
  
  <pre><code>import * as React from 'react';
  import { RouteComponentProps } from 'react-router';
  import { Link, NavLink } from 'react-router-dom';
  
  interface FetchPeriodDataState {
      periodList: PeriodData[];
      loading: boolean;
  }
  
  export class FetchPeriod extends React.Component&lt;RouteComponentProps&lt;{}&gt;, FetchPeriodDataState&gt; {
      constructor(props) {
          super(props);
      this.state = { periodList: [], loading: true };
  
  
      fetch('api/Period/Index')
          .then(response =&gt; response.json() as Promise&lt;PeriodData[]&gt;)
          .then(data =&gt; {
              this.setState({ periodList: data, loading: false });
          });
  
      // This binding is necessary to make "this" work in the callback  
      this.handleDelete = this.handleDelete.bind(this);
      this.handleEdit = this.handleEdit.bind(this);
  }
  </code></pre>
  
  <p>And then later on I have the PeriodData class:</p>
  
  <pre><code>export class PeriodData {
  PeriodId: number = 0;
  Description: string = "";
  PeriodOwner: string = "";
  PeriodName: string = "";}
  </code></pre>
  
  <p>The <code>this.state</code> and <code>this.setState</code> methods are giving the errors in the title, and I can't seem to find a fix.</p>