function formIsDirty(form) {
 for (var i = 0; i < form.elements.length; i++) {
  var element = form.elements[i];
  var type = element.type;
  if (type == "checkbox" || type == "radio") {
   if (element.checked != element.defaultChecked) {
    return true;
   }
  }
  else if (type == "hidden" || type == "password" ||
       type == "text" || type == "textarea") {
   if (element.value != element.defaultValue) {
    return true;
   }
  }
  else if (type == "select-one" || type == "select-multiple") {
   for (var j = 0; j < element.options.length; j++) {
    if (element.options[j].selected !=
      element.options[j].defaultSelected) {
     return true;
    }
   }
  }
 }
 return false;
}

window.onbeforeunload = function(e) {
 e = e || window.event; 
 if (formIsDirty(document.forms["someForm"])) {
  // For IE and Firefox
  if (e) {
   e.returnValue = "You have unsaved changes.";
  }
  // For Safari
  return "You have unsaved changes.";
 }
};

Click on below button. Now change some values in form and click the button again. <form name="fooForm">     <input type="text" name="t"><br>     <input type="text" name="2" value="default"><br>     <select name="some">         <option value="fooo" selected="">foo</option>         <option value="bar">bar</option>     </select><br> </form>     <button onclick="alert(formIsDirty(document.fooForm))">Click to check if Form is Dirty</button> <br> <script> function formIsDirty(form) {   for (var i = 0; i < form.elements.length; i++) {     var element = form.elements[i];     var type = element.type;     if (type == "checkbox" || type == "radio") {       if (element.checked != element.defaultChecked) {         return true;       }     }     else if (type == "hidden" || type == "password" ||              type == "text" || type == "textarea") {       if (element.value != element.defaultValue) {         return true;       }     }     else if (type == "select-one" || type == "select-multiple") {       for (var j = 0; j < element.options.length; j++) {         if (element.options[j].selected !=             element.options[j].defaultSelected) {           return true;         }       }     }   }   return false; } </script>