I'm using Javascript to change a form's URL when you submit the form. If that URL contains a hash string (#), then Internet Explorer ignores it and just submits to the part of the html before that. Firefox and Chrome are fine.

Demonstration:

<script type="text/javascript">
function changeURL() {
    var myform = document.getElementById('myform');

    myform.setAttribute("action", "page2.html#hello"); 

    return false;
}
</script>

<form id="myform" action="page1.html" method="get" onsubmit="changeURL()">
    <input type="submit">
</form>

If I change the method to a "post" then it's fine. If I use a "get", IE lands on page2.html but without the #hello in the URL.

This happens regardless of if I use jquery or only javascript, tried each of the following:

myform.action = "page2.html#hello";

myform.attr("action", "page2.html#hello");

myform.get(0).setAttribute("action", "page2.html#hello");

Any suggestions (assume that I have to keep the method as a 'get', and that I must use a hash in the URL, and that I must use Javascript to change this action dynamically)?

Testing on my own in IE8 reveals that it does insist that the hash (#hello) come after the query string (?foo=bar) in a URL. Sadly, your form doesn't do this for you and there's no way to force it to do so when submitting the form.

Try encoding the hash in the form instead:

<script type="text/javascript">
function changeURL() {
    var hidden = document.createElement('input');
    hidden.setAttribute("type", "hidden");
    hidden.setAttribute("name", "hash");
    hidden.setAttribute("value", "hello");
    var myform = document.getElementById('myform');
    myform.setAttribute("action", "page2.html");
    myform.appendChild(hidden);
    // return false;
}
</script>
<form id="myform" action="page1.html" method="get" onsubmit="changeURL()">
    <input type="submit">
</form>

And at the top of page2.html, extract it back out:

<script type="text/javascript">
var qs = window.location.search.substring(1);
var qsarr = qs.split("&");
for (var i=0; i<qsarr.length; i++) {
    var tarr = qsarr[i].split("=");
    if (tarr[0]==="hash") {
        window.location.hash = tarr[1];
    }
}
</script>