Update/Save list item edits without closing editform

I am working with a customised list 'editform' and would like to give my users the ability to save their edits without the editform closing, which is the default SP 'Save' behaviour.

I have linked the following code to a HTML button on my form, which appears to be going through the saving motions but refreshing the underlying list shows that the edits made were not saved.
  

function updateListItem() {

    var clientContext = new SP.ClientContext($url);
    var oList = clientContext.get_web().get_lists().getByTitle('Manage Recruitment Process Tasks');

    this.oListItem = oList.getItemById($myID);

    oListItem.set_item('Advertisement_x0020_Date', $adDate.val());

    oListItem.update();

    clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));
    }

    function onQuerySucceeded() {

    alert('Item updated!');
    }

    function onQueryFailed(sender, args) {

    alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
    }

The variable $url is set to '/sites/dev' and the variable $myID is set to the list item ID.  The code is getting through to 'oListItem.update();' but no further, without the onQuerySucceeded() or onQueryFailed() functions triggering.

Is there a syntax error in the code?

Thanks

Simon