Symbol.toStringTag

js

let user = {
  [Symbol.toStringTag]: "User",
};

({}).toString.call(user); // [object User]

js 地表最强类型检查：

js

const toString = Object.prototype.toString;

toString.call([]); // [object Array]
toString.call(1); // [object Number]
toString.call(true); // [object Boolean]
toString.call("哈哈"); // [object String]

toString.call(new Map()); // [object Map]
toString.call(new Date()); // [object Date]

toString.call(null); // [object Null]
toString.call(undefined); // [object Undefined]