Onload select variation doesn't changes the image?

<script type="text/javascript">
$( document ).ready(function() {
$('div.wpsc_variation_forms select.wpsc_select_variation')
.val('8')
.trigger('change');

});
</script>

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By using the above script i’m able to change the price and select the non default option, but the problem is that the image is not swapped according to the changed variation value.
Please help.

https://www.ads-software.com/extend/plugins/sp-wpec-variation-image-swap/