title: How to check if a multidimensional array item is set in JS?
body: <p>How to check if a multidimensional array item is set in JS?</p>
  
  <pre><code>w[1][2] = new Array;
  w[1][2][1] = new Array;
  w[1][2][1][1] = 10; w[1][2][1][2] = 20; w[1][2][1][4] = 30;
  </code></pre>
  
  <p>How to check if <code>w[1][2][1][3]</code> is set?</p>
  
  <p>Solution with <code>if (typeof w[1][2][1][3] != 'undefined')</code> doesn't work.</p>
  
  <p>I don't want to use an Object instead of Array.</p>