JavaScript和python的深浅拷贝最近一直在纠结这个问题，决定彻底搞懂深浅拷贝，为了方便理解和记忆，决定将py

最近一直在纠结这个问题，决定彻底搞懂深浅拷贝，为了方便理解和记忆，决定将python和js放在一起探讨下。

首先看下直接用'='赋值两种语言的表现。

JavaScript:

var l1 = [['js','python'],12,{"name":"jack"}]
var l2 = l1
l1.push('emmmmm')
l1[0].push('go')
console.log('l1',l1)
console.log('l2',l2)
console.log('l1 === l2:',l1 === l2)
/*
输出：
l1 [ [ 'js', 'python', 'go' ], 12, { name: 'jack' }, 'emmmmm' ]
l2 [ [ 'js', 'python', 'go' ], 12, { name: 'jack' }, 'emmmmm' ]
l1 === l2: true
*/

Python:

l1 = [['js','python'],12,{"name":"jack"},(13,14)]
l2 = l1

l1.append('emmmmm')
l1[0].append('go')
print('l1',l1)
print('l2',l2)
print('l1 is l2',l1 is l2)
'''
输出：
l1 [['js', 'python', 'go'], 12, {'name': 'jack'}, (13, 14), 'emmmmm']
l2 [['js', 'python', 'go'], 12, {'name': 'jack'}, (13, 14), 'emmmmm']
l1 is l2 True
'''

毫无疑问：用等号赋值就是直接指向拷贝对象，两者完全相同

浅拷贝

用构造器实现浅拷贝

JavaScript实现浅拷贝的几种方式:

数组浅拷贝array.slice()

var l1 = [['js','python'],12,{"name":"jack"}]
var l2 = l1.slice()
l1.push('emmmmm')
l1[0].push('go')
console.log('l1',l1)
console.log('l2',l2)
console.log('l1 === l2:',l1 === l2)

/*
l1 [ [ 'js', 'python', 'go' ], 12, { name: 'jack' }, 'emmmmm' ]
l2 [ [ 'js', 'python', 'go' ], 12, { name: 'jack' } ]
l1 === l2: false
*/

Object.assign()——ES6语法

var l1 = [['js','python'],12,{"name":"jack"}]
var l2 = Object.assign(l1)
l1.push('emmmmm')
l1[0].push('go')
console.log('l1',l1)
console.log('l2',l2)
console.log('l1 === l2:',l1 === l2)

/*
输出：
l1 [ [ 'js', 'python', 'go' ], 12, { name: 'jack' }, 'emmmmm' ]
l2 [ [ 'js', 'python', 'go' ], 12, { name: 'jack' }, 'emmmmm' ]
l1 === l2: true
*/

扩展符...

var l1 = [['js','python'],12,{"name":"jack"}]
console.log(...l1)
l1.push('emmmmm')
l1[0].push('go')
console.log(...l1)

/*
输出：
[ 'js', 'python' ] 12 { name: 'jack' }
[ 'js', 'python', 'go' ] 12 { name: 'jack' } 'emmmmm'
*/

Python:

l1 = [['js','python'],12,{"name":"jack"},(13,14)]
l2 = list(l1)

l1.append('emmmmm')
l1[0].append('go')
l1[3] += (15,16)
print('l1',l1)
print('l2',l2)
print('l1 is l2',l1 is l2)
'''
输出：
l1 [['js', 'python', 'go'], 12, {'name': 'jack'}, (13, 14, 15, 16), 'emmmmm']
l2 [['js', 'python', 'go'], 12, {'name': 'jack'}, (13, 14)]
l1 is l2 False
'''

可以看出，python、JavaScript的拷贝都是浅拷贝：即子元素都是拷贝对象子元素的引用。

比较特殊的是python存在元组这种类型，元组是不可变的，因此l1对元组的操作实际上是创建了一个新元组，而l2并没有重新指向新元组。

深拷贝

深度拷贝，是指重新分配一块内存，创建一个新的对象，并且将原对象中的元素，以递归的方式，通过创建新的子对象拷贝到新对象中。因此，新对象和原对象没有任何关联。

Python：

import copy
l1 = [['js','python'],12,{"name":"jack"},(13,14)]
l2 = copy.deepcopy(l1)

l1.append('emmmmm')
l1[0].append('go')
l1[3] += (15,16)
print('l1',l1)
print('l2',l2)
print('l1 is l2',l1 is l2)
'''
输出：
l1 [['js', 'python', 'go'], 12, {'name': 'jack'}, (13, 14, 15, 16), 'emmmmm']
l2 [['js', 'python'], 12, {'name': 'jack'}, (13, 14)]
l1 is l2 False
'''

JavaScript实现深拷贝的几种方式：

JSON.parse/stringify

这种方法适用于：对象中不包含Date函数，undefined，Infinity，正则，映射，集合，Blob，FileLists，ImageDatas，稀疏数组，类型化数组或其他复杂类型。如果包含了上述类型，深拷贝会出现偏差

const a = {
    string: 'string',
    number: 123,
    bool: false,
    nul: null,
    date: new Date(),  // stringified
    undef: undefined,  // lost
    inf: Infinity,  // forced to 'null'
    re: /.*/,  // lost
  }
  console.log(a);
  console.log(typeof a.date);  // Date object
  const clone = JSON.parse(JSON.stringify(a));
  console.log(clone);
  console.log(typeof clone.date);  // result of .toISOString()
  
/*
输出：
{ string: 'string',
  number: 123,
  bool: false,
  nul: null,
  date: 2019-09-02T03:25:11.116Z,
  undef: undefined,
  inf: Infinity,
  re: /.*/ }
object
{ string: 'string',
  number: 123,
  bool: false,
  nul: null,
  date: '2019-09-02T03:25:11.116Z',
  inf: null,
  re: {} }
string

*/

使用一些库的深拷贝函数

loadsh.cloneDeep()

const loadsh = require('loadsh')

const a = {
    string: 'string',
    number: 123,
    bool: false,
    nul: null,
    date: new Date(),  // stringified
    undef: undefined,  // lost
    inf: Infinity,  // forced to 'null'
    re: /.*/,  // lost
}

const clone = loadsh.cloneDeep(a)

console.log(a)
console.log(clone)

/*
输出：
{ string: 'string',
  number: 123,
  bool: false,
  nul: null,
  date: 2019-09-02T07:21:57.823Z,
  undef: undefined,
  inf: Infinity,
  re: /.*/ }
{ string: 'string',
  number: 123,
  bool: false,
  nul: null,
  date: 2019-09-02T07:21:57.823Z,
  undef: undefined,
  inf: Infinity,
  re: /.*/ }
*/

angular.copy()

// Module: copyExample
angular.
  module('copyExample', []).
  controller('ExampleController', ['$scope', function($scope) {
    $scope.leader = {};

    $scope.reset = function() {
      // Example with 1 argument
      $scope.user = angular.copy($scope.leader);
    };

    $scope.update = function(user) {
      // Example with 2 arguments
      angular.copy(user, $scope.leader);
    };

    $scope.reset();
  }]);