整理JS如何判断数据类型

// 初始化一些变量

var num = 123;

var str = 'abcdef';

var bool = true;

var arr = [1, 2, 3, 4];

var obj = {name:'wenzi', age:25};

var func = function(){ console.log('this is function'); }

var und = undefined;

var nul = null;

var date = new Date();

var reg = /^[a-zA-Z]{5,20}$/;

var error= new Error();

typeof num,  // number

typeof str,  // string

typeof bool,  // boolean

typeof arr,  // object

typeof obj,  // object

typeof func,  // function

typeof und,  // undefined

typeof nul,  // object

typeof date,  // object

typeof reg,  // object

typeof error // object

    num instanceof Number, // false

    str instanceof String, // false

    bool instanceof Boolean,  // false

    arr instanceof Array, // true--注意

    arr instanceof Object, // true--注意

    obj instanceof Object,  // true--注意

    func instanceof Function,  // true

    und instanceof Object, // false

    nul instanceof Object, // false

    date instanceof Date,  // true

    reg instanceof RegExp, // true

    error instanceof Error // true

    Object.prototype.toString.call(num),  // '[object Number]'

    Object.prototype.toString.call(str),  // '[object String]'

    Object.prototype.toString.call(bool),  // '[object Boolean]'

    Object.prototype.toString.call(arr),  // '[object Array]'

    Object.prototype.toString.call(obj),  // '[object Object]'

    Object.prototype.toString.call(func),  // '[object Function]'

    Object.prototype.toString.call(und),  // '[object Undefined]'

    Object.prototype.toString.call(nul),  // '[object Null]'

    Object.prototype.toString.call(date),  // '[object Date]'

    Object.prototype.toString.call(reg),  // '[object RegExp]'

    Object.prototype.toString.call(error)  // '[object Error]'

function Person(){}

var Tom = new Person();

// undefined和null没有constructor属性

console.log(

    Tom.constructor==Person,

    num.constructor==Number,

    str.constructor==String,

    obj.constructor==Boolean,

    arr.constructor==Array,

    json.constructor==Object,

    func.constructor==Function,

    date.constructor==Date,

    reg.constructor==RegExp,

    error.constructor==Error

);

// 所有结果均为true

const obj = { [Symbol("a")]: 1 }

console.log(Object.keys(obj))

console.log(JSON.stringify(obj))

console.log(Reflect.ownKeys(obj))