使用constructor属性来查看对象是否为日期（包含字符串'

 var mdate = new Date();
    console.log(isDate(mdate));

    function isDate(mdate) {
        let fn = mdate.constructor;
        let str = fn.toString();
        let ar = str.indexOf("Date") != -1;
        return fn +' ******* '+ str+'----'+ar
    }

运行结果如下：