javascript自定义日期格式化

<script>
    Date.prototype.formateDate=function(){
        var str="";
        str+=this.getFullYear()+"年";
        str+=(this.getMonth()+1)+"月";
        str+=this.getDate()+"日";
        return str;
    }
    var date=new Date();
    alert(date.formateDate());
</script>