title: JS, how to append array in FormData?
body: <p>i hope append array in js FormData.</p>
  
  <p>like this,</p>
  
  <pre><code>var fd = new FormData();
  fd.append("key", new Array(["a","b","c"]));
  console.log(fd.get("key"));
  </code></pre>
  
  <p>the result is,</p>
  
  <pre><code>a,b,c
  </code></pre>
  
  <p>result type is 'String'...</p>
  
  <p>i want to parse "aa" array in java(JSONArray).</p>
  
  <p>please help me.</p>