title: Javascript add extra argument
body: <p>Let's take a look at this code:</p>
  <pre><code>var mainFunction = function() {
    altFunction.apply(null, arguments);
  }
  </code></pre>
  <p>The arguments that are passed to <code>mainFunction</code> are dynamic -- they can be 4 or 10, doesn't matter. However, I have to pass them through to <code>altFunction</code> AND I have to add an EXTRA argument to the argument list.</p>
  <p>I have tried this:</p>
  <pre><code>var mainFunction = function() {
    var mainArguments = arguments;
    mainArguments[mainArguments.length] = 'extra data'; // not +1 since length returns &quot;human&quot; count.
  
    altFunction.apply(null, mainArguments);
  }
  </code></pre>
  <p>But that does not seem to work. How can I do this?</p>