1

我试图弄清楚下面处理将一个对象复制到另一个对象的代码中发生了什么。在某些情况下，它们就像同一个对象，改变一个对象会改变另一个对象。我发现了很多关于如何通过引用复制 javascript 对象的帖子，因此它们实际上是同一个对象。例如，来自http://www.w3schools.com/js/js_object_definition.asp：

 var person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"} 
 var x = person;  // This will not create a copy of person. 
 x.age = 10; // This will change both x.age and person.age

 The object x is not a copy of person. It is person. Both x and person
 is the same object. Any changes to x will also change person, because
 x and person are the same object.

但是，我还发现了一个对象似乎是单独对象的情况。它如何在一种情况下表现得像同一个对象，但在另一种情况下表现得像不同的对象？我将不胜感激任何情况：

示例： http ://codepen.io/gratiafide/pen/yagQGr?editors=1010#0

HTML：

<div id="app">
  <my-component>
  </my-component>
</div>

JS：

  var MyComponent = Vue.extend({
  template: '<div v-on:click="test()" class="red">1.  Click here to copy the name object to message and change the value of name to see if the value of message gets changed also.  (It does not).</div>  message: {{ message | json}} <br> name: {{ name | json}}<div v-on:click="test2()" class="red">2.  Now click here to see if updating  the name object also changes the message object.  It does!  Why here and not in #1?</div><div v-on:click="test3()" class="red">3.  Click here to see yet another way of updating the name object also changes the message object. Why here and not in #1?</div>',

  data: function () {
    return { 
    message: {},
    name: {}
    }
  },

  ready: function(){
    this.message = {};
  },
  methods: {
    test: function(){
       this.message = {'t1':"m1"};
       this.name = this.message;  
       this.name = {'t2':"m2"};  
    },
    test2: function(){
       this.message = {'t1':"m1"};
       this.name = this.message;  
       for (var key in this.name) {
                this.name[key] = '';
            }  
    },
    test3: function(){
       this.message = {'t1':"m1"};
       this.name = this.message;  
       Vue.set(this.name, 't1', 'm2');
    }
  }
});

Vue.component('my-component', MyComponent);

new Vue({
  el: '#app'
});

CSS：

@import url(https://fonts.googleapis.com/css?family=Open+Sans);

.red{
  color:red;  
}

body {
  font-family: 'Open Sans', sans-serif;
  background: rgba(0,0,0,.5);
  margin: 0;
}

#app {
  width: 500px;
  margin: 0 auto;
  padding: 10px 20px;
  background: rgba(255,255,255,.9);
}
4

2 回答 2

2

基本上，您要问这三个之间的区别：

this.message = {'t1':"m1"};
this.name = this.message;  

#1:
this.name = {'t2':"m2"};  

#2
for (var key in this.name) {
  this.name[key] = '';
}  

#3
Vue.set(this.name, 't1', 'm2');

在第一种情况下，您不会更改this.message，因为您将一个全新的对象分配给this.name. 这个新对象 ( {'t2':"m2"}) 与 完全无关this.message。

也许您正在尝试/想要做的是：

this.name.t2 = "m2";

#2 和 #3 的作用相同，影响this.message，因为this.name 仍然指的是同一个对象。

要将新属性分配给现有对象，从另一个对象，您可以Object.assign在支持此功能的浏览器中使用：

Object.assign(this.name, {'t2':"m2"});
于 2016-09-24T02:56:04.220 回答
1

有两种类型的变量，值和引用。所有原语（即字符串、数字和布尔值）都按值存储，其他所有内容都通过引用存储并且可以具有属性。

var a,b;
a={c:1};
b=a;
console.log (b===a); // true;

b={c:1}; // note that b is now being assigned a new reference.
console.log (b===a); // false;

a=b; // now a is being assigned the reference of b.
console.log (b===a); // true;

a.c=2; //note that it is the property of a (c) got changed, not a itself.
console.log (b===a); // true;

a.a = a; //now a has a property (a) that stores the reference of a.
console.log(a === a.a);
console.log(a.a === a.a.a);
console.log(a.a === a.a.a.a.a.a.a.a.a);
a.a.a.a.a.a.a.a.a.a.a.c = 10;
console.log(a.c)//10;
There are different ways to declare variables, but that isn't the scope of the question.

于 2016-09-24T04:01:04.640 回答