引用类型对象拷贝

引用类型有哪些？非引用类型有哪些

• 引用类型值（对象、数组、函数、正则）：指的是那些保存在堆内存中的对象，变量中保存的实际上只是一个指针，这个指针执行内存中的另一个位置，由该位置保存对象。

    var a;
    var b;
    var obj;
    var obj2;


    a = 1;
    b = 2;

    var obj = {
        name: 'ruoyu',
        sex: 'male',
        age: 30,
        friend: {
            name: 'hello', 
            age: 100
        }
    }

    var newObj = {};



    b = a;
    console.log(b);

    var obj2 = obj;


    var obj3 = {name: 'hello'};
    var obj4 = {name: 'hello'};
    obj3 === obj4



    function sum(){
        console.log('sum...')
    }
    var sum2 = sum;
    sum2()

• 非引用类型
  对象浅拷贝和深拷贝

//浅拷贝

    function shallowCopy(oldObj) {
        var newObj = {};
        for(var i in oldObj) {
            if(oldObj.hasOwnProperty(i)) {
                newObj[i] = oldObj[i];
            }
        }
        return newObj;
    }

//深拷贝

    function deepCopy(oldObj) {
        var newObj = {};
        for(var key in oldObj) {
            if(typeof oldObj[key] === 'object') {
                newObj[key] = deepCopy(oldObj[key]);
            }else{
                newObj[key] = oldObj[key];
            }
        }
        return newObj;
    }

如下代码输出什么？为什么

var obj1 = {a:1, b:2};
var obj2 = {a:1, b:2};
console.log(obj1 == obj2);//false obj1和obj2为两个对象，存储在位置不同，不相等
console.log(obj1 = obj2);//[object Object] {
  a: 1,
  b: 2
} ；
//将obj2赋值给obj1，此时obj1和obj2在同一个位置，console.log输出obj1的值，即object {a:1, b:2}

console.log(obj1 == obj2);//true，此时obj1和obj2在同一个位置，因此为true

如下代码输出什么? 为什么

var a = 1
var b = 2
var c = { name: '饥人谷', age: 2 }
var d = [a, b, c]

var aa = a
var bb = b
var cc = c
var dd = d

a = 11
b = 22
c.name = 'hello'
d[2]['age'] = 3//c和cc存储地址内容更新为{name: 'hello', age: 3}

console.log(aa) //1
console.log(bb) //2
console.log(cc)// age: 3, name: "hello"。
console.log(dd)//[1, 2, {name: 'hello', age: 3}]

如下代码输出什么? 为什么

var a = 1
var c = { name: 'jirengu', age: 2 }

function f1(n){
  ++n
}

function f2(obj){       // var obj = c
  ++obj.age             // obj = { name: 'jirengu', age: 3 }
}                       // c =  { name: 'jirengu', age: 3 }    

f1(a) 
f2(c) 
f1(c.age) 
console.log(a) //1
console.log(c)//age: 3,name: "jirengu"

过滤如下数组，只保留正数，直接在原数组上操作

var arr = [3,1,0,-1,-3,2,-5]
function filter(arr){
for (var i = 0; i < arr.length; i++) {
            if (arr[i] < 1) {
                arr.splice(i,1);
                filter(arr)
             }
        } 
     }
    filter(arr)
    console.log(arr) // [3,1,2]

过滤如下数组，只保留正数，原数组不变，生成新数组

var arr = [3,1,0,-1,-3,2,-5]
function filter(arr){
var arr2 = [];
    function filter(arr) {
        for (var i = 0; i < arr.length; i++) {
            if (arr[i] > 0) {
                arr2.push(arr[i]);
            }
        }
    }
    filter(arr)
    console.log(arr2) // [3,1,2]
    console.log(arr)  // [3,1,0,-1,-2,2,-5]

写一个深拷贝函数，用两种方式实现

var obj = {
        age: 24,
        friend: {
            name: 'simin',
            sex: 'female',
        }
    }
//方法1
function copy(obj) {
        var obj2 = {}
        for (var key in obj) {
            if (obj.hasOwnProperty(key)) {
                if (typeof obj[key] === 'number'
                    || typeof obj[key] === 'string'
                    || typeof obj[key] === 'boolean'
                    || obj[key] === undefined
                    || obj[key] === null) {
                    obj2[key] = obj[key]
                } else {
                    obj2[key] = copy(obj[key])
                }
            }
        }
        return obj2
    }
    var newobj1 = copy(obj)
    console.log(newobj1)

//方法2
function deepcopy(obj) {
        var newobj2 = JSON.parse(JSON.stringify(obj));
        return newobj2;
    }
    obj.age = 30
    console.log(deepcopy(obj))