var imgs = new Array();

function eventSet(obj, heads, tails) {
	// マウスオーバー
	obj.onmouseover = function() {
		obj.src = heads;
	}
	// マウスアウト
	obj.onmouseout = function() {
		obj.src = tails;
	}
}

function swapImage(selector, heads, tails) {
	imgs.push(heads, tails);
	// idセレクタ
	if(document.getElementById(selector)) {
		var obj = document.getElementById(selector);
		eventSet( obj, heads, tails );
	// classセレクタ
	} else if(document.getElementsByClassName(selector)) {
		for(i=0; i<document.getElementsByClassName(selector).length; i++) {
			var obj = document.getElementsByClassName(selector)[i];
			eventSet(obj, heads, tails);
		}
	}
}

function preload() {
	var img = new Array();
	for(var i=0; i<imgs.length; i++) {
		img[i] = new Image();
		img[i].src = imgs[i];
	} 
}