typeof的探讨

    console.log(typeof 'abc') // "string"
    console.log(typeof true )// "boolean"
    console.log(typeof {a:1}) // "object"
    console.log(typeof function foo(){}) // "function"
    console.log(typeof undefined) // "undefined"
    console.log(typeof Symbol('foo')) // "symbol" es6新增类型

//    typeof 检测数据类型，返回值是字符串
    console.log(typeof 123) // 返回"number"
    console.log(typeof typeof 123)// 返回时string
    console.log(typeof NaN) // "number"
    console.log(typeof [1,2,3])// "object"

//    判断Array object和Object object
    console.log(Array.isArray([1,2,3]))// true
    console.log(Array.isArray({a:1}))// false

    console.log(typeof null) // "object"

    console.log(typeof class Foo{}) // "function"