title: Javascript: Getting all existing keys in a JSON array
body: <p>I have a JSON array like below:</p>
  
  <pre><code>var jsonArray = [{"k1":"v1"},{"k2":"v2"},{"k3":"v3"},{"k4":"v4"},{"k5":"v5"}]
  </code></pre>
  
  <p>I don't know which keys does exists in this array. 
  I want to get all the existing key from the array.</p>
  
  <p>It should be possible something like this:</p>
  
  <pre><code>for(i=0;i&lt;jsonArray.lenght;i++){
    // something like-  key = jsonArray[i].key
    // alert(key);
  }
  </code></pre>
  
  <p>Please tell me the method or way to get all keys existing in Json array.</p>
  
  <p>Regards</p>