function $(id) {
    return document.getElementById(id);
}
function $$(name) {
    var elements = document.getElementsByName(name);
    
    elements.check = function(checked) {
        for (var i = 0; i < elements.length; i++) {
            elements[i].checked = checked ? 'checked' : '';
        }
    };
    return elements;
}

var Ajax = {
    'getHTTPObject': function() {
        var xmlhttp = false;
        try {
            xmlhttp = new ActiveXObject("Msxm12.XMLHTTP");
        }
        catch (e) {
            try {
                xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (E) {
                xmlhttp = false
            }
        }
        if (!xmlhttp && typeof XMLHttpRequest != 'undefined') {
            xmlhttp = new XMLHttpRequest();
        }
        return xmlhttp;
    },
    'get' : function(url, callback){
	    var xmlhttp = Ajax.getHTTPObject();
	    if(!xmlhttp){
		    return;
	    }
	    //给url加一个随机数，在下次访问是避免缓存的干扰
	    //indexof---查找url中是否存在？，没有的话返回-1
	    if(url.indexOf('?') == -1){
		    url += '?';
	    }
	    url += '&tmp=' + Math.random();
	    xmlhttp.open("GET", url);
	    xmlhttp.onreadystatechange = function(){
		    if(xmlhttp.readyState == 4 && xmlhttp.status == 200){
			    if(callback){
				    callback(xmlhttp.responseText);
			    }
		    }
	    }
	    xmlhttp.send(null);
    }
};

// 修复 IE 下 PNG 图片不能透明显示的问题
function fixPNG(myImage) {
    var arVersion = navigator.appVersion.split("MSIE");
    var version = parseFloat(arVersion[1]);
    if ((version >= 5.5) && (version < 7) && (document.body.filters)) {
        var imgID = (myImage.id) ? "id='" + myImage.id + "' " : "";
        var imgClass = (myImage.className) ? "class='" + myImage.className + "' " : "";
        var imgTitle = (myImage.title) ? "title='" + myImage.title + "' " : "title='" + myImage.alt + "' ";
        var imgStyle = "left:5px;position:absolute;cursor:pointer;";
        var strNewHTML = "<span " + imgID + imgClass + imgTitle
                    + " style=\"" + "width:" + myImage.width
                    + "px; height:" + myImage.height
                    + "px;" + imgStyle + ";"
                    + "filter:progid:DXImageTransform.Microsoft.AlphaImageLoader"
                    + "(src=\'" + myImage.src + "\', sizingMethod='scale');\"></span>";
        myImage.outerHTML = strNewHTML;
    }
}