console.log(typeof null)
console.log(typeof undefined)
console.log(typeof "123")
console.log(typeof true)
console.log(typeof 123)
console.table([1,2,3,])
console.log("一个未声明的变量", typeof aaa)
var result = undefined == null;
console.log("相等性测试 undefinde == null 的结果是", result)