title: Fetch() API not updating JSON file
body: <p>I have a JSON file I want to read from and write to that looks like this:</p>
  
  <pre><code>[
      "test@example.com"
  ]
  </code></pre>
  
  <p>I want to add info to this file using the <code>fetch()</code> API. So far, I can only read from this file.</p>
  
  <pre><code>let handle = JSON.stringify(`test@example2.com`); // handle is fine irrelevant of "" or ``
  const url = `../json/emails.json`; // URL is fine
  const options = {
      method: `POST`, // PUT return error at second fetch: SyntaxError: "JSON.parse: unexpected character at line 1 column 1 of the JSON data"
      headers: {
          'Accept': 'application/json',
          'Content-Type': 'application/json'
      },
      body: handle
  };
  
  fetch(url) // this fetch is fine
      .then(response =&gt; {
          if (!response.ok) {
              throw new Error(`Error getting the stuff`);
          }
          return response;
      })
      .then(r =&gt; r.json())
      .then(data =&gt; {
          console.log(`Data: ` + data);
      });
  
  fetch(url, options)
      .then(response =&gt; {
          if (!response.ok) {
              throw new Error(`Error getting the stuff`);
          }
          return response;
      })
      .then(a =&gt; a.json())
      .then(append =&gt; {
          console.log(`Data updated: ` + append);
      }).catch(err =&gt; {
          console.error('Request failed: ', err);
      });
  </code></pre>
  
  <p>I get no errors (aside from that <code>PUT</code> comment); ESLint and TSLint don't have any problem with the JS file nor with the JSON file. What am I doing wrong?</p>