title: how can i prevent onbeforeunload from firing when a certain condition is met?
body: <p>i have a page on which i want to confirm if the user wants to leave.
  i have to confirm only when a certain condition is met so i wrote code like this</p>
  
  <pre><code>var back=false;
  back=//check if user pressed back button
  window.onbeforeunload = function (e) {
      alert(back);   //this alerts true
      if(back==true)
          return false;
          //e.preventDefault;   --this does not work too
  };
  </code></pre>
  
  <p>but this does not work. i mean when i click on back button this onbeforeunload still fires and i still get the confirmation message even when i m returning false.Whats can be wrong?
  Thanks </p>