title: What is theForm.onsubmit()?
body: <p>can someone explain this function for me. What do <code>!theForm.onsubmit()</code> and <code>theForm.onsubmit() != false</code> mean?</p>
  
  <pre><code>//&lt;![CDATA[
  var theForm = document.forms['Form'];
  if (!theForm) {
      theForm = document.Form;
  }
  function __doPostBack(eventTarget, eventArgument) {
      if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
          theForm.__EVENTTARGET.value = eventTarget;
          theForm.__EVENTARGUMENT.value = eventArgument;
          theForm.submit();
      }
  }
  //]]&gt;
  </code></pre>
  
  <p>And when I checked with the console I got this;</p>
  
  <pre><code>!theForm.onsubmit
  true
  theForm.onsubmit
  null
  !null
  true
  </code></pre>
  
  <p>What is the meaning of <code>theForm.onsubmit</code>, how can it be <code>null</code> and <code>!null</code> be true? </p>
  
  <p>And when I checked <code>theForm.onsubmit() != false</code> I got:</p>
  
  <pre><code>theForm.onsubmit()
  TypeError: object is not a function
  theForm.onsubmit() != false
  TypeError: object is not a function
  </code></pre>
  
  <p>What is the difference by the way between <code>theForm.onsubmit</code> and <code>theForm.onsubmit()</code>?</p>