title: Javascript undefined condition
body: <p>Could somebody explain to me the difference between <code>if(obj.x == undefined)</code> and <code>if(typeof obj.x == 'undefined')</code></p>
  
  <p>In some context the first one works fine, but in other I need to use the second way.</p>
  
  <p>Questions</p>
  
  <p>1 - What is the difference between the two condition?</p>
  
  <p>2 - Is there a best practice?</p>