nickpartyka

Figured it out on my own. This is the working code:

<script type="text/javascript">
	<!--
	var dropdown = document.getElementById("cat");
	function onCatChange() {
		if ( dropdown.options[dropdown.selectedIndex].value == 0 ) {
			location.href = "<?php echo esc_url( home_url( '/' ) ); ?>blog";
		}
		else if ( dropdown.options[dropdown.selectedIndex].value > 0 ) {
			location.href = "<?php echo esc_url( home_url( '/' ) ); ?>?cat="+dropdown.options[dropdown.selectedIndex].value;
		}
	}
	dropdown.onchange = onCatChange;
	-->
</script>