title: No 'Access-Control-Allow-Origin' - CORS
body: <p>I try to fetch content via <code>XMLHttpRequest</code>:  </p>
  
  <pre><code>var url = 'http://mapy.geoportal.gov.pl/wss/service/SLN/guest/sln/woj.json'
  
      if (XMLHttpRequest) {
      var request = new XMLHttpRequest();
      if ('withCredentials' in request) {
          request.open('GET', url, true);
          request.withCredentials = 'true';
          request.withCredentials = 'true';
          request.setRequestHeader('Access-Control-Allow-Origin', '*');
          request.send();
      }
  }
  </code></pre>
  
  <p>I am getting next message: </p>
  
  <blockquote>
    <p>XMLHttpRequest cannot load
    <a href="http://mapy.geoportal.gov.pl/wss/service/SLN/guest/sln/woj.json" rel="nofollow noreferrer">http://mapy.geoportal.gov.pl/wss/service/SLN/guest/sln/woj.json</a>.
    Response to preflight request doesn't pass access control check: No
    'Access-Control-Allow-Origin' header is present on the requested
    resource. Origin 'null' is therefore not allowed access.</p>
  </blockquote>
  
  <p>How to fix this? I set <code>Access-Control-Allow-Origin</code> header to <code>*</code></p>
  
  <p>continu my problem with url : <a href="https://stackoverflow.com/questions/36112000/uncaught-syntaxerror-unexpected-token-when-use-jsonp">jsonp continue</a></p>