title: TypeError: NetworkError when attempting to fetch resource
body: <p>I obtain this problem :</p>
  
  <pre><code>Response { type: "cors", url: "http://localhost:3000/api/marks",
  redirected: false, 
  status: 200, 
  ok: true, 
  statusText: "OK", 
  headers: Headers, 
  body: ReadableStream, 
  bodyUsed: true }
  MarkService.js:5
  Cross-Origin Request Blocked: 
  The Same Origin Policy disallows reading the remote resource at      
  http://localhost:3000/api/marks. (Reason: CORS request did not succeed). 
  </code></pre>
  
  <p>This is where it points</p>
  
  <pre><code>class MarkService {
    constructor() {
      this.URI = `localhost:3000/api/marks`;
    }
  
    async getMarks() {
      const response = await fetch(this.URI);
      const marks = await response.json();
      return marks;
    }
  }
  export default MarkService;
  </code></pre>
  
  <p>I'm trying to make a app with express in the backend and Webpack for the frontend.
  I have a Rest API in the backend and I can't use it on the frontend.</p>
  
  <p>I'm using Ubuntu with Mozilla Firefox 66.0.2 and Nodejs 11.13.0</p>
  
  <p>When I use the console, it said that the problem is in it</p>