Select List innerHTML

Javascript

function switch_Select(pThis,pThat){
// destination select
var l_That = document.getElementById(pThat);

// value from first select
var l_ThisValue = pThis.options[ pThis.selectedIndex ].value

// this would be the string returned from AJAX call
// the colons separate the options
// the commas separate the label and value of each option element
var l_testString = 'county 1,V1:county 2,V2:county 3,V3:county 4,V4';

// create array with element for each option
var l_testArray = l_testString.split(":");

// only get array length once because it's slightly faster;
var l_Array_Length =  l_testArray.length;

// clear destination select
l_That.options.length = 0;

// add option nodes into destination select
	for(var i=0; i < l_Array_Length; i++) {
		// split array element to get option label and option value
		var l_TempArray = l_testArray[ i ].split(",");
		var l_newValue = l_ThisValue + '-' + l_TempArray[ 0 ];
		var l_newReturn = l_TempArray[ 1 ];
		l_That.options[ i ] = new Option(l_newValue,l_newReturn);
	}

}

</script>

Select List without innerHTML

Javascript