title: for( … in …) not working with array
body: <p>I'm somehow confused:</p>
  
  <p>I have a list of commands like this:</p>
  
  <pre><code>var commands = [{"command": "read"}, {"command": "write"}, {"command": "login"}];
  </code></pre>
  
  <p>If I try it access one of the commands like this it works:</p>
  
  <pre><code>console.log(commands[0]["command"]); // Output is "read"
  console.log(commands[0].command);    // Output is "read"
  </code></pre>
  
  <p>But if I try this the output is always undefined:</p>
  
  <pre><code>for(command in commands)
      console.log(command["command"]); // undefined, undefined, undefined
  </code></pre>