javascript - OnUnload Alert Error "NS_ERROR_NOT_AVAILABLE" - 


<html> <body>  <button type="button" onclick="clickme()">click me</button>  <script> var test = 0;  function clickme() {   test = 1;   console.log(test); }  window.onunload = function() {   alert("test"); } </script>  </body> </html>

i'm using simple code test things onunload , onbeforeunload. reason whenever refresh/leave page , cause onunload event no alert , error in firebug console. if use onbeforeunload works , no error, hear onbeforeunload isn't cross-browser.

ns_error_not_available: component returned failure code: 0x80040111      (ns_error_not_available) [nsidomwindow.alert]  alert("test");

i not trying alert test variable, text "test" before tries point out.

if want work, have in onbeforeunload event, instead of creating alert/confirm pop-up, onbeforeunload event has built in pop-up. have return string , pop-up appear when user tries navigate away page. if there no return variable, there no pop-up.

  • the great thing pop-up message has 2 buttons: ok , cancel.
  • if user hits ok, browser continue navigate away page
  • if user hits cancel, browser cancel unload , stay on current page
  • the onbeforeunload event pop-up can cancel onunload event

an example below:

<script type="text/javascript">  window.onbeforeunload=before; window.onunload=after;  function before(evt) {    return "this appear in dialog box along other default text";    //if return statement not here, other code executed silently (with no pop-up) }  function after(evt) {    //this event fires fast application execute before browser unloads }  </script>

it seems trying alert in onunload event. issue here it's late. page unloading , there no stopping it. may able alert message show, doesn't matter user clicks because page unloading.

your best bet go onbeforeunload event.


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