title: What is the meaning of || in javascript?
body: <p>I am looking at these lines of code from <a href="https://github.com/jacomyal/sigma.js/blob/master/plugins/sigma.parsers.cypher/sigma.parsers.cypher.js#L184-186" rel="noreferrer">here</a>:</p>
  
  <pre><code>    if (callback)
          callback(sig || graph);
  </code></pre>
  
  <p>I have never see vertical "or" bars in a javascript method call. What do they mean? Do they pass the "true" parameter (i.e. sig or graph)? Do they pass the defined parameter? I have never seen that syntax before.</p>