How can I stop HTML form from reloading the page [duplicate]

You need to use the preventDefault() method of the event object.

Note that neither addEventListener() nor preventDefault() are supported in IE <= 8.

var form = document.forms[0]; 
form.addEventListener("submit", function(evt){
  var email = form.elements['answer_13829'].value;
  if( email == '[email protected]') {
     evt.preventDefault();
     alert('redirecting the user...');
     window.location = 'xxxx';
  }
});