title: Check if value exists in JavaScript object
body: <p>How would I check in my array of objects, if a specific item exists (in my case MachineId with id 2)?</p>
  
  <pre><code>[{"MachineID":"1","SiteID":"20"},{"MachineID":"2","SiteID":"20"},{"MachineID":"3","SiteID":"20"},{"MachineID":"4","SiteID":"20"}]
  </code></pre>
  
  <p>I tried this:</p>
  
  <pre><code>if (index instanceof machineIds.MachineID) {
      alert('value is Array!');
  } else {
      alert('Not an array');
  }
  </code></pre>