title: JavaScript null; placeholder vs "ready for purging"
body: <p>Just read some material that stated 'null' in javascript can be used as a placeholder. But then it moved on to saying that 'null' can also indicate that a certain variable is ready for purging. But how does javascript know whether a variable with null is currently acting as a placeholder and not "ready for purging"... or vice versa?</p>
  
  <p>Any pointers would be appreciated.</p>