title: Meaning of variable in array as property name?
body: <pre><code>var expertise = 'journalism'
  var person = {
      name: 'Sharon',
      age: 27,
      [expertise]: {
          years: 5,
          interests: ['international', 'politics', 'internet']
      }
  }
  </code></pre>
  
  <p>In this expression, why are we considering <code>[expertise]</code> in brackets as property name? What's the need to put bracket?</p>