Javascript通过引用或按值分配数组元素

Question

有没有办法通过引用而不是通过值显式设置数组元素？

例如，此方法通过值设置数组元素：

方法1

var pushes = [2,1]
for(var i=0; i<pushes.length; i++)
{
   vm.allEmployeesOnJob[i] = vm.allEmployees[pushes[i]];                  
}

并且此方法通过引用设置数组元素：

方法2

var pushes = [2,1]
vm.allEmployeesOnJob = [
                vm.allEmployees[2],
                vm.allEmployees[1]                
              ];

我的用例：

我正在使用angular-bootstrap-duallistbox，为了正确初始化两个列表框，“ ng-model”数组必须通过引用引用“ ng-options”数组元素。 这是由于我已阅读的说明中的“ select” DOM元素的行为所致。 我知道第二个是通过引用设置的原因是因为列表框使用该方法可以正确更新，而使用第一个方法则不能正确更新。

有什么区别？

有没有一种方法可以通过编程将数组元素以编程方式设置为另一个数组的元素？

编辑：

vm.allEmployees是一组雇员对象。

vm.allEmployees的内容：

[      {  
      "employeeId":1,
      "firstName":"Bill",
      "lastName":"Test",
      "email":null,
      "phoneNumber":null,
      "street":"1234 Sesame",
      "city":"New York City",
      "state":"New York",
      "zip":"34555",
      "activeFlag":true,
      "homeLocationId":2,
      "homeLocation":{  
         "locationId":2,
         "customerId":2,
      },
      "displayName":"Bill Test - Newaygo"    },    
 {  
      "employeeId":2,
      "firstName":"Bob",
      "lastName":"Test",
      "email":null,
      "phoneNumber":null,
      "street":"1234 Sesame",
      "city":"New York City",
      "state":"New York",
      "zip":"34555",
      "activeFlag":true,
      "homeLocationId":2,
      "homeLocation":{  
         "locationId":2,
         "customerId":2,
      },
      "displayName":"Bob Test -  Newaygo"    },    
 {  
      "employeeId":4,
      "firstName":"John",
      "lastName":"Doe",
      "email":"testemployee@qas.com",
      "street":"1234 Sesame St",
      "city":"New York City",
      "state":"New York",
      "zip":"34555",
      "activeFlag":true,
      "homeLocationId":2,
      "homeLocation":{  
         "locationId":2,
         "customerId":2,
      },
      "displayName":"John Doe -  Newaygo"    },    
 {  
      "employeeId":5,
      "firstName":"Bill",
      "lastName":"Peterson",
      "email":"bpeterson@test.com",
      "street":"1234 test",
      "city":"test city",
      "state":"Maine",
      "zip":"298379283",
      "activeFlag":false,
      "homeLocationId":2,
      "homeLocation":{  
         "locationId":2,
         "customerId":2,
      },
      "displayName":"Bill Peterson -  Newaygo"    },    
 {  
      "employeeId":6,
      "firstName":"Jim",
      "lastName":"Super",
      "email":"jsuper@qas.com",
      "phoneNumber":"459-456-4455",
      "street":"1234 Sesame St",
      "city":"New York City",
      "state":"New York",
      "zip":"34555",
      "activeFlag":true,
      "homeLocationId":2,
      "homeLocation":{  
         "locationId":2,
         "customerId":2,
      },
      "displayName":"Jim Super -  Newaygo"    } ]

Answer 1

在JavaScript中，对象是通过引用引用的，而所有其他值（无论它们是否在数组中）都是通过值引用的。 您可以将值存储在对象中，如果需要获得此行为，则可以引用/传递该值。

您下面的两种方法都可以使用对象，并且具有“按引用”引用。 这两个摘要验证：

方法1

 var vm = {}; // Here, the contents of the array are ojbects (by reference) vm.allEmployees = [ { "employeeId":1, "firstName":"Bill", "lastName":"Test", "email":null, "phoneNumber":null, "street":"1234 Sesame", "city":"New York City", "state":"New York", "zip":"34555", "activeFlag":true, "homeLocationId":2, "homeLocation":{ "locationId":2, "customerId":2, }, "displayName":"Bill Test - Newaygo" }, { "employeeId":2, "firstName":"Bob", "lastName":"Test", "email":null, "phoneNumber":null, "street":"1234 Sesame", "city":"New York City", "state":"New York", "zip":"34555", "activeFlag":true, "homeLocationId":2, "homeLocation":{ "locationId":2, "customerId":2, }, "displayName":"Bob Test - Newaygo" }, { "employeeId":4, "firstName":"John", "lastName":"Doe", "email":"testemployee@qas.com", "street":"1234 Sesame St", "city":"New York City", "state":"New York", "zip":"34555", "activeFlag":true, "homeLocationId":2, "homeLocation":{ "locationId":2, "customerId":2, }, "displayName":"John Doe - Newaygo" }, { "employeeId":5, "firstName":"Bill", "lastName":"Peterson", "email":"bpeterson@test.com", "street":"1234 test", "city":"test city", "state":"Maine", "zip":"298379283", "activeFlag":false, "homeLocationId":2, "homeLocation":{ "locationId":2, "customerId":2, }, "displayName":"Bill Peterson - Newaygo" }, { "employeeId":6, "firstName":"Jim", "lastName":"Super", "email":"jsuper@qas.com", "phoneNumber":"459-456-4455", "street":"1234 Sesame St", "city":"New York City", "state":"New York", "zip":"34555", "activeFlag":true, "homeLocationId":2, "homeLocation":{ "locationId":2, "customerId":2, }, "displayName":"Jim Super - Newaygo" } ] vm.allEmployeesOnJob = []; var pushes = [2,1] for(var i=0; i<pushes.length; i++) { vm.allEmployeesOnJob[i] = vm.allEmployees[pushes[i]]; } // The references are by reference: console.log("Are objects in allEmployeesOnJob the same references as allEmployees: " + (vm.allEmployeesOnJob[0] === vm.allEmployees[2] && vm.allEmployeesOnJob[1] === vm.allEmployees[1])); // More evidence: vm.allEmployees[2].employeeId= 999; console.log("allEmployees[2].employeeId= 999. allEmployeesOnJob[0].employeeId is now: " + vm.allEmployeesOnJob[0].employeeId); 

方法2

 var vm = {}; vm.allEmployees = [ { "employeeId":1, "firstName":"Bill", "lastName":"Test", "email":null, "phoneNumber":null, "street":"1234 Sesame", "city":"New York City", "state":"New York", "zip":"34555", "activeFlag":true, "homeLocationId":2, "homeLocation":{ "locationId":2, "customerId":2, }, "displayName":"Bill Test - Newaygo" }, { "employeeId":2, "firstName":"Bob", "lastName":"Test", "email":null, "phoneNumber":null, "street":"1234 Sesame", "city":"New York City", "state":"New York", "zip":"34555", "activeFlag":true, "homeLocationId":2, "homeLocation":{ "locationId":2, "customerId":2, }, "displayName":"Bob Test - Newaygo" }, { "employeeId":4, "firstName":"John", "lastName":"Doe", "email":"testemployee@qas.com", "street":"1234 Sesame St", "city":"New York City", "state":"New York", "zip":"34555", "activeFlag":true, "homeLocationId":2, "homeLocation":{ "locationId":2, "customerId":2, }, "displayName":"John Doe - Newaygo" }, { "employeeId":5, "firstName":"Bill", "lastName":"Peterson", "email":"bpeterson@test.com", "street":"1234 test", "city":"test city", "state":"Maine", "zip":"298379283", "activeFlag":false, "homeLocationId":2, "homeLocation":{ "locationId":2, "customerId":2, }, "displayName":"Bill Peterson - Newaygo" }, { "employeeId":6, "firstName":"Jim", "lastName":"Super", "email":"jsuper@qas.com", "phoneNumber":"459-456-4455", "street":"1234 Sesame St", "city":"New York City", "state":"New York", "zip":"34555", "activeFlag":true, "homeLocationId":2, "homeLocation":{ "locationId":2, "customerId":2, }, "displayName":"Jim Super - Newaygo" } ] var pushes = [2,1] vm.allEmployeesOnJob = [ vm.allEmployees[2], vm.allEmployees[1] ]; console.log("Are objects the same (by ref)? " + (vm.allEmployeesOnJob[0] === vm.allEmployees[2] && vm.allEmployeesOnJob[1] === vm.allEmployees[1])); // Further evidence: vm.allEmployees[2].employeeId = 999; console.log("allEmployees[2].employeeId was changed to 999. What is allEmployeesOnJob[0].employeeId now? " + vm.allEmployeesOnJob[0].employeeId);