1.引用类型有对象、数组、函数、正则，非引用类型有数值、布尔值、null、undefined

var obj1 = {a:1, b:2};
var obj2 = {a:1, b:2};
console.log(obj1 == obj2);//false 因为obj1,obj2是引用类型，里面只存储着地址并不相等
console.log(obj1 = obj2);//{a:1,b:2}将obj2赋值给obj1，使obj1的指针也指向obj2的地址
console.log(obj1 == obj2);//true，obj1,obj2指向同一个地址

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

console.log(aa) //1
console.log(bb) //2
console.log(cc)//{ name: 'hello, age: 3 },cc和c指向同一地址，
console.log(dd)//{2，1，name: 'hello, age: 3}同上

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

function f1(n){
  ++n
}
function f2(obj){
  ++obj.age
}

f1(a) 
f2(c) 
f1(c.age) 
console.log(a) //1,将n赋值a,a是原始类型不会改变a的值
console.log(c)//{ name: 'jirengu', age: 3 }，f2(c)使c中国的age变为3，而f1(c.age) 不会改变c中的age

5.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]<=0){
                  arr.splice(i,1);
                       filter(arr);
                    } 
              }
       }
      filter(arr);
      console.log(arr); // [3,1,2]

6.过滤如下数组，只保留正数，原数组不变，生成新数组

1.  var arr = [3,1,0,-1,-3,2,-5];
        var arr2 = arr.filter(function(elem){
            return (elem > 0);
        });
        alert(arr2);
        alert(arr);     

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

7.写一个深拷贝函数，用两种方式实现

function deepCopy(obj){
var newobj={}
for(var key in obj){
      if(typeof obj[key] ==  "string"|| typeof obj[key] ==  "number" ||  obj[key] ==   undefined ||
        obj[key] ==  null || typeof obj[key] ==  "boolean"){
        newobj[key] = obj[key];
      }else{
        newobj[key] = deepCopy(obj[key]);
      }
    }
  return newobj;
}
var obj = {
  name:"jirengu",
  age:2
}
var obj2 = deepCopy(obj);
console.log(obj2);
obj.age = 26;
console.log(obj2.age);
//
function deepCopy2(obj){
  return JSON.parse(JSON.stringify(obj));
}
var obj3 = {
  name:"ruoyu",
  age:20
}
var obj4 = deepCopy2(obj3);
console.log(obj4);
obj3.age = 27;
console.log(obj4.age);