var number = 5;
var number_copy = number;
/*number和number_copy中的值是相互独立的，两个变量可以任意操作而不互相影响
*/

var object = {name: 'ckn', age: 18};
var object_copy = object;
object_copy.name = 'lxh';
/*复制的是引用，复制结束后，两个变量实际上引用的还是同一个对象修改其中任何一个变量，都会影响另外一个变量
*/

function log(target){return console.log(target);
}
log(typeof 110); // number
log(typeof 'hello world'); // string
log(typeof true); // boolean
log(typeof undefined); // undefined
log(typeof null);  // object
log(typeof {name: 'ckn', age: 18}); // object
log(typeof [1,2,3,4]); // object 我们其实期望得到的是array
log(typeof function() {log(1)}) // function
// 我们可以通过 Array.isArray()来判断其是否是数组
// 或者我们也可以 instanceof 来判断属于哪一类对象
log([1,2,3,4] instanceof Array); // true

function log(target){return console.log(target);
}
function whatType(target){return Object.prototype.toString.call(target).slice(8, -1);
}
log(whatType(110)); // Number
log(whatType('hello world')); // String
log(whatType(true)); // Boolean
log(whatType({name: 'ckn',age: 18})); // Object
log(whatType([1,2,3,4])); // Array
log(whatType(function(){log(1)})); // Function
log(whatType(undefined));  // Undefined
log(whatType(null)); // Null
log(whatType(/z-Z/)); RegExp
log(whatType(new Date())); // Date

let obj = {name: 'ckn', age: 18}
/*obj是Object构造函数的实例对象 obj.toString方法是继承自Objectconsole.log(obj.toString === Object.prototype.toString);  true
*/
console.log(obj.toString()); // 这个很重要 它打印出的是[object Object]
/*arr是Array构造函数的实例对象 arr.toString方法是继承自Arrayconsole.log(arr.toString === Array.prototype.toString);  true
*/
let arr =  [1,2,3];
console.log(array.toString()); // "1,2,3,4" 字符串形式
/*bar是Function构造函数的实例对象 bar.toString方法是继承自Functionconsole.log(bar.toString === Function.prototype.toString);  true
*/
let bar = function() { console.log('hello world') }
console.log(bar.toString()); // "function() { console.log('hello world') }"// 其实根据MDN的解释，我们还可以自定义obj的toString方法 这样就不会继承来自Object的toString方法了
obj.prototype.toString = function toStringSelf() {return `your name is ${this.name}, your age is ${this.age}`
}
obj.toString(); // your name is ckn, your age is 18/*
console.log(bar.toString);
ƒ (){return"function"==typeof this&&this.__raven__?t._originalFunctionToString.apply(this.__orig__,arguments):t._originalFunctionToString.apply(this,arguments)}
*/

Object.prototype.toString.call(target)

Function.prototype.toString.call({name:'ckn', age:18});
// Uncaught TypeError:Function.prototype.toString requires that 'this' be a FunctionFunction.prototype.toString.call(function() {});
//  "function() {}"Number.prototype.toString.call({name:'ckn', age:18});
// Uncaught TypeError:Number.prototype.toString requires that 'this' be a Number
Number.prototype.toString.call(101);
// "101"

Array.prototype.toString.call(function(){}); // "[object Function]"
Array.prototype.toString.call({name: 'ckn',age: 18}); // "[object Object]"
Array.prototype.toString.call(new Date); // "[object Date]"
Array.prototype.toString.call([1,function(){},{}]); // "1,function(){},[object Object]"Array.prototype.toString.call(undefiend);
// Uncaught TypeError: Cannot convert undefined or null to objectArray.prototype.toString.call(null);
// Uncaught TypeError: Cannot convert undefined or null to object

Object.prototype.toString.call(undefined); // "[object Undefined]"
Object.prototype.toString.call(null); // "[object Null]"Object.prototype.toString.call(function(){}); // "[object Function]"
Object.prototype.toString.call({name: 'ckn',age: 18}); // "[object Object]"
Object.prototype.toString.call(new Date); // "[object Date]"
Object.prototype.toString.call([1,function(){},{}]); // "[object Array]"
Object.prototype.toString.call(/z-Z/); // "[object RegExp]"

function whatType(target) {reutnr Object.prototype.toString.call(target).slice(8, -1);
}