HTML5 placeholder label模拟法半透明交互实例页面

HTML代码：

<label for="email">邮箱:</label>
<input id="email" type="email" placeholder="zhangxinxu@zhangxinxu.com" size="26" />

JS代码：

var funPlaceholder = function(element) {
    var placeholder = "";
    //检测是否需要模拟placeholder
    if (element && !("placeholder" in document.createElement("input")) && (placeholder = element.getAttribute("placeholder"))) {
        //当前文本控件是否有id, 没有则创建
        var idLabel = element.id ;
        if (!idLabel) {
            idLabel = "placeholder_" + new Date().getTime();
            element.id = idLabel;
        }
        
        //创建label元素
        var eleLabel = document.createElement("label");
        eleLabel.htmlFor = idLabel;
        eleLabel.style.position = "absolute";
        //根据文本框实际尺寸修改这里的margin值
        eleLabel.style.margin = "2px 0 0 3px";
        eleLabel.style.color = "graytext";
        eleLabel.style.cursor = "text";
        
        //插入创建的label元素节点
        element.parentNode.insertBefore(eleLabel, element);
        
        //方法
        var funOpacity = function(ele, opacity) {
            if (ele.style.opacity) {
                ele.style.opacity = opacity / 100;
            } else {
                ele.style.filter = "Alpha(opacity="+ opacity +")";    
            }
        }, opacityLabel = function() {
            if (element.value === "") {
                funOpacity(eleLabel, 40);
                eleLabel.innerHTML = placeholder;
            } else {
                eleLabel.innerHTML = "";    
            }
        };
        
        //事件
        element.onkeyup = function() { opacityLabel(); };
        element.onfocus = function() { opacityLabel(); };
        element.onblur = function() {
            if (this.value === "") {
                funOpacity(eleLabel, 100);
                eleLabel.innerHTML = placeholder;  
            }
        };
        
        //样式初始化
        if (element.value === "") { eleLabel.innerHTML = placeholder; }
    }    
};

funPlaceholder(document.getElementById("email"));