ie8 ie9兼容placeholder

<script type="text/javascript">
    if( !('placeholder' in document.createElement('input')) ){

        $('input[placeholder],textarea[placeholder]').each(function(){
            var that = $(this),
                text= that.attr('placeholder');
            if(that.val()===""){
                that.val(text).addClass('placeholder');
            }
            that.focus(function(){
                if(that.val()===text){
                    that.val("").removeClass('placeholder');
                }
            })
                .blur(function(){
                    if(that.val()===""){
                        that.val(text).addClass('placeholder');
                    }
                })
                .closest('form').submit(function(){
                if(that.val() === text){
                    that.val('');
                }
            });
        });
    }
</script>