console.log(typeof null);
console.log(typeof '');
console.log(typeof 123);
console.log(typeof '123 ');
var a = [1,2,3]
console.log(a);
console.log(a instanceof Array);
console.log(Array.isArray(a));
let o ={}
console.log(o);
let date = new Date()
console.log(date instanceof Date);
let reg = /133/
console.log(reg instanceof RegExp);
function fn(){}
console.log(fn instanceof Function);
console.log(toString.a);
console.log(Object.prototype.toString(a));
console.log(Object.prototype.toString.call(a));
console.log(Object.prototype.toString.call(null));
console.log(a.constructor == Array);
console.log(a.constructor == Object);