title: Why are preload link not working for JSON requests ?
body: <p>The JavaScript on my website loads several JSON to initialize itself.</p>
  
  <p>I would like to preload them so, when the JavaScript will launch an Ajax request on it, they will be loaded instantaneously.</p>
  
  <p>A new <a href="https://w3c.github.io/preload/" rel="noreferrer"><code>link</code></a> tag exists for that.</p>
  
  <p>I tried to use it to load a JSON like that :</p>
  
  <pre><code>&lt;link rel="preload" href="/test.json"&gt;
  </code></pre>
  
  <p>However, Chrome seems to load it twice and present a warning in the console : </p>
  
  <p><em>The resources test.json was preloaded using link preload but not used within a few seconds from the window's load event. Please make sure it wasn't preloaded for nothing.</em></p>
  
  <p>So it seems that preload doesn’t work for JSON.
  Indeed, I haven’t found reference to JSON in <a href="https://w3c.github.io/preload/#link-element-interface-extensions" rel="noreferrer">the specification</a>.</p>
  
  <p>Is that correct or am I doing it wrong ?</p>