js获取变量类型

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

let str = "Hello, world!";
console.log(typeof str); // 输出 "string"

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

let obj = { key: "value" };
console.log(typeof obj); // 输出 "object"

let arr = [1, 2, 3];
console.log(typeof arr); // 输出 "object"，注意数组也是对象

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

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

let nul = null;
console.log(typeof nul); // 输出 "object"，这是一个历史悠久的JavaScript bug

let symbol = Symbol("sym");
console.log(typeof symbol); // 输出 "symbol"

let bigint = BigInt(12345678901234567890n);
console.log(typeof bigint); // 输出 "bigint"

let arr = [1, 2, 3];
console.log(Array.isArray(arr)); // 输出 true

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