Send post-variable with javascript?

The simplest way is to just have a form in your page:

<form method="POST" action="hanteraTaBortAnvandare.php" id="DeleteUserForm">
<input type="hidden" name="id" value="10" />
</form>

Then you just post the form:

document.getElementById("DeleteUserForm").submit();

You can use a form and then document.getElementById('id_of_the_form').submit();

The form doesn't need to be wrote as plain HTML: you can create it dinamically:

     function postIt()   {
        form = document.createElement('form');
        form.setAttribute('method', 'POST');
        form.setAttribute('action', 'someURL');
        myvar = document.createElement('input');
        myvar.setAttribute('name', 'somename');
        myvar.setAttribute('type', 'hidden');
        myvar.setAttribute('value', 'somevalue');
        form.appendChild(myvar);
        document.body.appendChild(form);
        form.submit();   
}

You can do it with an Ajax-request (or use hidden forms) - in that case;

MooTools example:

new Request({
    url: 'hanteraTaBortAnvandare.php',
    method: 'post',
    data: {
        'id': '10'
    },
    onComplete: function(response) {
        alert(response);
    }
});

jQuery example:

$.ajax({
    type: 'post',
    url: 'hanteraTaBortAnvandare.php',
    data: 'id=10',
    success: function(response) {
        alert(response);
    }
});

Of course you could do this without external libraries, but they simplify alot!

You can submit form data via JavaScript but not using window.location.href. Changing the URL location is always going to issue a GET.

You'll need to get a reference to your form from the DOM and then issue a submit() call to it.

You can use the XMLHTTPRequest() object.