title: Ternary expression with a javascript object
body: <p>Let's say I have the following javascript object:</p>
  
  <pre><code>var __error__ = {0: 'ok'}
  </code></pre>
  
  <p>I want to return an empty string if the key is not in the obj, and an error message otherwise. For example:</p>
  
  <pre><code>var value = __error__[col_num] ? "The value cannot be converted" : ""
  </code></pre>
  
  <p>How could this be done with a ternary expression properly? Do I need to do <code>__error__[col_num] == undefined</code> ? Or does the above expression evaluate to <code>false</code> by itself?</p>