javascript - 为什么以及何时使用 angular.copy？ (深拷贝)

Question

我一直将从服务接收的所有数据直接保存到局部变量、 Controller 或范围。我想应该被认为是浅拷贝，对吗？

Example:

DataService.callFunction()
.then(function(response) {
  $scope.example = response.data;
});

最近我被告知要使用 angular.copy 来创建深拷贝。

$scope.example = angular.copy(response.data);

但是，当我的 Angular 应用程序使用深层复制信息时，它似乎以相同的方式工作。 使用深拷贝 (angular.copy) 有什么特别的好处吗？您能给我解释一下吗？

Answer 1

使用 angular.copy将对象或数组的值分配给另一个变量时，该 object 值不应更改。

没有深层复制或使用angular.copy，更改属性值或添加任何引用同一对象的新属性更新所有对象。

var app = angular.module('copyExample', []);
app.controller('ExampleController', ['$scope',
  function($scope) {
    $scope.printToConsole = function() {
      $scope.main = {
        first: 'first',
        second: 'second'
      };

      $scope.child = angular.copy($scope.main);
      console.log('Main object :');
      console.log($scope.main);
      console.log('Child object with angular.copy :');
      console.log($scope.child);

      $scope.child.first = 'last';
      console.log('New Child object :')
      console.log($scope.child);
      console.log('Main object after child change and using angular.copy :');
      console.log($scope.main);
      console.log('Assing main object without copy and updating child');

      $scope.child = $scope.main;
      $scope.child.first = 'last';
      console.log('Main object after update:');
      console.log($scope.main);
      console.log('Child object after update:');
      console.log($scope.child);
    }
  }
]);

// Basic object assigning example

var main = {
  first: 'first',
  second: 'second'
};
var one = main; // same as main
var two = main; // same as main

console.log('main :' + JSON.stringify(main)); // All object are same
console.log('one :' + JSON.stringify(one)); // All object are same
console.log('two :' + JSON.stringify(two)); // All object are same

two = {
  three: 'three'
}; // two changed but one and main remains same
console.log('main :' + JSON.stringify(main)); // one and main are same
console.log('one :' + JSON.stringify(one)); // one and main are same
console.log('two :' + JSON.stringify(two)); // two is changed

two = main; // same as main

two.first = 'last'; // change value of object's property so changed value of all object property 

console.log('main :' + JSON.stringify(main)); // All object are same with new value
console.log('one :' + JSON.stringify(one)); // All object are same with new value
console.log('two :' + JSON.stringify(two)); // All object are same with new value

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>

<div ng-app="copyExample" ng-controller="ExampleController">
  <button ng-click='printToConsole()'>Explain</button>
</div>