function placeholder(el){
            function isPlaceHolder(){
                var textarea = document.createElement("textarea");
                return "placeholder" in textarea;
            }
        debugger;
        var $el = $(el);
        //在不支持placeHolder屬性的情況下
        if(isPlaceHolder() == false && !('placeholder' in document.createElement('textarea'))){
            $('textarea[placeholder]').each(function(){
                var that = $(this);
                text = that.attr('placeholder');
                
                if(that.val()===""){
                    that.val(text).addClass('placeholder');
                }
                
                //獲得光標焦點後，輸入框的內容清空
                that.focus(function(){
                    if($el.html() == text){
                        $el.html("");
                    }
                    if(that.val() == text){
                        that.val("").removeClass('placeholder');
                    }
                }).blur(function(){
                    //光標焦點離開輸入框時，給輸入框添加提示內容
                    if(that.val() === ""){
                        
                        that.val(text).addClass('placeholder');
                    }
                })
            })
        }

    }
</script/>
 

-->

placeholder 不支持ie8