js如何获取变量的类型的

let num = 123;
console.log(typeof num); // 输出: "number"

let str = "Hello";
console.log(typeof str); // 输出: "string"

let bool = true;
console.log(typeof bool); // 输出: "boolean"

let undef;
console.log(typeof undef); // 输出: "undefined"

let func = function() {};
console.log(typeof func); // 输出: "function"

let obj = {};
console.log(typeof obj); // 输出: "object" (注意: null 也会返回 "object")

let nul = null;
console.log(typeof nul); // 输出: "object" (这是一个历史遗留问题)

let arr = [1, 2, 3];
console.log(Object.prototype.toString.call(arr)); // 输出: "[object Array]"

let date = new Date();
console.log(Object.prototype.toString.call(date)); // 输出: "[object Date]"

let nul = null;
console.log(Object.prototype.toString.call(nul)); // 输出: "[object Null]"

let obj = {};
console.log(Object.prototype.toString.call(obj)); // 输出: "[object Object]"

let nul = null;
console.log(Object.prototype.toString.call(nul) === '[object Null]'); // 输出: true