How can I run a Greasemonkey script when page changed via ajax?

I have that script:

// ==UserScript==
// @name     example
// @include  http://xxx*
// @require  http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js
// ==/UserScript==

var findElem = function(elems, text) {
    for (var i = 0; i < elems.length; i++) {
        if (elems[i].textContent == text) {
            return elems[i];
        } else {
            var result = findElem(elems[i].children, text);
            if (result != undefined) {
                return result;
            }
        }
    }
    return;
}

switch (document.getElementById('my_id').value) {
    case "1":
        findElem(document.documentElement.children, "blabla1").click();
        break;
    case "2":
        findElem(document.documentElement.children, "blabla2").click();
        break;
    case "3":
        findElem(document.documentElement.children, "blabla3").click();
        break;
    case "4":
        findElem(document.documentElement.children, "blabla4").click();
        break;
    default:
        break;
}

It works fine but it works only main page load. I want to run this when page changed via ajax. How can I do that?

Also please give examples with your answers. I’m newbie. I don’t know how to use things in your answers.

Answer

Since browser’s environment is event-driven you’ll have to either set up a timer, bind to some event that happens around update you looking for. Alternatively, you can wrap function that does update and call your code in post-hook. Obviously, you’ll need to wrap your userscript code in some function to reuse.

Here’s an example with timer set up with setInterval (top of script is still the same):

setInterval(function(){
    switch (document.getElementById('my_id').value) {
        case "1":
            findElem(document.documentElement.children, "blabla1").click();
            break;
        case "2":
            findElem(document.documentElement.children, "blabla2").click();
            break;
        case "3":
            findElem(document.documentElement.children, "blabla3").click();
            break;
        case "4":
            findElem(document.documentElement.children, "blabla4").click();
            break;
        default:
            break;
    }
}, 1000) // if AJAX updates happen with some specific interval, set same number here to minimize useless work