How to change the background image of a label using CSS with JavaScript

Question

This one is a real headache. I have three checkboxes in a form that I have labels for, and the labels have background images set with CSS, the question is, how exactly do I get my JavaScript to change the image from current image to a second image when it is clicked and select the checkbox. From what I know of javascript, it should work, any ideas? Also, it does have to be this way due to previous issues with i.e. 7 and 8.

HTML

<input type="checkbox" name="interest1" id="interest1" value="interested"style="display:block">
<input type="checkbox" name="interest2" id="interest2" value="interested"style="display:block">
<input type="checkbox" name="interest3" id="interest3" value="interested"style="display:block">
<p align="center">
<label for="interest_inet" id="label-interest1" onClick="func()"></label>

CSS:

label {
    border:1px solid red;
    display:inline-block;
}

#label-interest1 {
    background-image: url(images/internetbutton.gif);
    width: 152px;
    height:152px;
}

JavaScript:

<script type="text/javascript">
function func()
{
    if(document.getElementById('interest_inet').checked)
    {
        document.getElementById('label-interest1').style.backgroundImage=url(images/internetbutton.gif);
    }
    else
    {
        document.getElementById('label-interest1').style.backgroundImage=url(internetbuttonchecked.gif);
    }
}
</script>

Here is a live code example

Solution

You seem to just be missing some quotes (the value of style.backgroundImage should be a string):

function func()
{
    var label = document.getElementById('label-interest1');
    if(document.getElementById('interest_inet').checked)
    {
        label.style.backgroundImage = 'url(images/internetbutton.gif)';
    }
    else
    {
        label.style.backgroundImage = 'url(internetbuttonchecked.gif)';
    }
}