keyType(data) {

      let type = Object.prototype.toString.call(data);

      if (type === "[object String]") {

        type = "String";

      } else if (type === "[object Number]") {

        type = "Number";

      } else if (type === "[object Null]") {

        type = "Null";

      } else if (type === "[object Boolean]") {

        type = "Boolean";

      } else if (type === "[object Array]") {

        type = "Array";

      } else if (type === "[object Object]") {

        type = "Object";

      } else {

        type = "未进行判断的类型:" + type;

      }

      return type;

    },

如：

let arr = [1，2，3]; 

let type = this.keyType();

console.log("判断的类型", type);