title: Why assigning to const variable does not lead to an error?
body: <p>Demo: <a href="http://jsfiddle.net/rmrG9/" rel="nofollow">http://jsfiddle.net/rmrG9/</a></p>
  
  <p>Code:</p>
  
  <pre><code>const a = 10
  a = 20
  alert('a: ' + a)
  </code></pre>
  
  <p>The output is:</p>
  
  <pre><code>a: 10
  </code></pre>
  
  <p>Can you explain why the statement <code>a = 20</code> did not throw an error?</p>