js 数组的浅拷贝和深拷贝

var arr1 = [1, 2, 3, 4];
var arr2 = arr1; 
arr1[0] = 6;                //数组是用堆去保存的，相等的时候只是把存放的地址拷贝过去了，两个指向了同一个地址，所以在改变其中一个的值，其他的也跟着改变了
console.log(arr2[0]);       //输出结果为6
console.log(arr1);        //[6, 2, 3, 4]
console.log(arr2);        //[6, 2, 3, 4]

var arr1 = [1, 2, 3, 4];
var arr2 = JSON.parse(JSON.stringify(arr1)) //先将数组转为字符串，然后转成js对象

arr1[0] = 6; 
console.log(arr2[0]);       //输出结果为1
console.log(arr1);        //[6, 2, 3, 4]
console.log(arr2);        //[1, 2, 3, 4]

var arr1 = [1, 2, 3, 4];
var arr2 = arr1.slice(0);   //从0开始到末尾截取数组，然后返回一个新的数组
arr1[0] = 6; 
console.log(arr2[0]);       //输出结果为1
console.log(arr1);        //[6, 2, 3, 4]
console.log(arr2);        //[1, 2, 3, 4]

var arr1 = [1, 2, 3, 4];
var arr2 = arr1.concat();   //连接数组，如果连接的是一个空，那么也是返回了新的本身的数组
arr1[0] = 6; 
console.log(arr2[0]);       //输出结果为1
console.log(arr1);        //[6, 2, 3, 4]
console.log(arr2);        //[1, 2, 3, 4]

var arr1 = [1, 2, 3, 4]; 
var arr2 = arr1.map(function(value){
     return value;
})                          //使用map方法遍历数组然后返回新的数组，里面的值不变
arr1[0] = 6;   
console.log(arr2[0])        //输出结果为1
console.log(arr1);          //[6, 2, 3, 4]
console.log(arr2);          //[1, 2, 3, 4]

var arr1 = [1, 2, 3, 4];
var [ ...arr2 ] = arr1;     //ES6扩展运算符实现数组的深拷贝
arr1[0] = 6; 
console.log(arr2[0]);       //输出结果为1
console.log(arr1);        //[6, 2, 3, 4]
console.log(arr2);        //[1, 2, 3, 4]

var arr1 = [1, 2, 3, 4];
var arr2 = [];
for(i=0;i<arr1.length;i++){
　　arr2.push(arr1[i])
}

arr1[0] = 6; 
console.log(arr2[0]);       //输出结果为1
console.log(arr1);        //[6, 2, 3, 4]
console.log(arr2);        //[1, 2, 3, 4]