title: checking if isNan in a condition
body: <p>I'm doing some JavaScript self-study, trying to check if n is anything other than a number in the third if of the factorial function, but I can't get it to work. Any help would be appreciated</p>
  
  <pre><code>var factorial = function(n) {
      // Update so that all tests pass
      if (n &gt; 20) {
          return undefined;
      }
      if (n === 1) {
          return 1;
      }
      if(isNan(n)){
          return undefined;
      }
      return n * factorial(n-1);
  };
  </code></pre>