How to run code after changing the URL via [remove

Question

I'm doing this but it doesn't work:

window.addEventListener("load", function load(event){
    alert('hola');
},false);

window.location.assign("about:blank");

It's a Greasemonkey script. The new location is loaded but the alert is never shown.

Answer 1

By only changing the hash (or fragment) part of the url, then doing whatever it is you want to do, thus:

window.location.assign("#hello")
alert("hola")

or thus:

window.location.hash = "world"
alert("mondo")

If the document has already loaded, onload will not trigger again, so you cannot run it from a load event. HTML5, offers a hashchange event, which you could use, thus:

window.addEventListener("hashchange", function (event){
    alert('change');
},false);

Some javascript libraries (I know dojo does) implement hashchange or an equivalent for non-HTML5 browsers. In order to take advantage of that, you would need to use that library's convention for registering for events.

Answer 2

Once you change the window.location, the current instance of your Greasemonkey script is purged. To "run code" after the location change, you need to set the script to trigger on the new page (about:blank in this case), and then use a flag to signal that the new page was reached via this script redirecting the original page.

1. Make sure that the script's @include or @match directives fire on the new page.
2. Use GM_setValue() to set the flag letting the script know it has been deliberately reincarnated.

Here is a complete, working script that illustrates the process:

// ==UserScript==
// @name     _Fire after redirect to about:blank
// @include  about:blank
// @include  http://YOUR_SERVER.COM/YOUR_PATH/*
// @require  http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js
// @grant    GM_setValue
// @grant    GM_getValue
// @grant    GM_deleteValue
// ==/UserScript==

//-- Are we on a blank page after a redirect by this script?
var bAfterRedirect = GM_getValue ("YouHaveBeenRedirected", false);

//-- Always erase the stored flag.
GM_deleteValue ("YouHaveBeenRedirected");

if (bAfterRedirect  &&  location == 'about:blank') {
    //-- DO WHATEVER YOU WANT WITH THE BLANK/NEW PAGE HERE.
    $("body").append (
        '<h1>This content was added after a GM redirect.</h1>'
    );
}
else if (location != 'about:blank') {
    /*-- If we are on the original target page, signal our next incarnation
        that it was triggered by a redirect.  Then redirect to about:blank.
    */
    GM_setValue ("YouHaveBeenRedirected", true);
    location.assign ("about:blank");
}