select元件使用輪滾

wheel.js

function wheelSelect(event) {
  event.preventDefault();
	var intMax = event.target.options.length - 1;
	var intIndex = event.target.selectedIndex;
	var intNextIndex = 0;
	if(event.detail > 0) {
		//wheel down
		if((intIndex + 1) <= intMax) intNextIndex = intIndex + 1;
		else intNextIndex = 0;
	} else {
		//wheel up
		if((intIndex - 1) >= 0) intNextIndex = intIndex - 1;
		else intNextIndex = intMax;
	}
	event.target.options[intNextIndex].selected = true;
};

var sels = document.getElementsByTagName('select');
for(var i = 0; i < sels.length; i++) {
	sels[i].addEventListener('DOMMouseScroll', wheelSelect, false);
};