title: is there some method of array like set in python?
body: <p>As I know in python i can set a list to a unique list like: </p>
  
  <pre><code>In [12]: a=range(12)
  
  In [13]: a.append(5)
  
  In [14]: a.append(4)
  
  In [15]: a.append(5)
  
  In [16]: a
  Out[16]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 5, 4, 5]
  
  In [17]: set(a)
  Out[17]: set([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11])
  </code></pre>
  
  <p>it is very useful  for some scene,
  i just want to know how to this in javascript,</p>