title: fetch() does not send headers?
body: <p>I am sending POST request like this from browser:</p>
  
  <pre><code>fetch(serverEndpoint, {
      method: 'POST',
      mode: 'no-cors', // this is to prevent browser from sending 'OPTIONS' method request first
      redirect: 'follow',
      headers: new Headers({
              'Content-Type': 'text/plain',
              'X-My-Custom-Header': 'value-v',
              'Authorization': 'Bearer ' + token,
      }),
      body: companyName
  })
  </code></pre>
  
  <p>By the time the request reaches my back-end it does not contain <code>X-My-Custom-Header</code> nor <code>Authorization</code> header. </p>
  
  <p>My back-end is Google Cloud function for Firebase (basically just Node.js endpoint) that looks like this:</p>
  
  <pre><code>exports.createCompany = functions.https.onRequest((req, res) =&gt; {
      let headers = ['Headers: ']
      for (let header in req.headers) {
          headers.push(`${header} : ${req.headers[header]}`)
      }
      console.log(headers)
      ...
  }
  </code></pre>
  
  <p>The console log of that Google Cloud for Firebase function does not contain any <code>X-My-Custom-Header</code> nor <code>Authorization</code> header.</p>
  
  <p>What is wrong?</p>
  
  <hr>
  
  <h2>Edit 1</h2>
  
  <p>So using dev tools in Chrome a checked that neither <code>X-My-Custom-Header</code> nor <code>Authorization</code> header is send from the browser... The questions now are: Why? How do I fix it?</p>
  
  <hr>
  
  <h2>Edit 2</h2>
  
  <p>More information about my app: It's React app. I have disabled service worker. I have tried to create <code>Request</code> and specifically add headers using <code>req.headers.append()</code>. The headers still wouldn't send. </p>