javascript - 在一种情况下是相同的对象，在另一种情况下是不同的对象？

Question

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一样，改变一个就会改变另一个。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，我也发现了对象看起来是独立对象的情况。它怎么能在一种情况下表现得像同一个对象，而在另一种情况下表现得像不同的对象呢？如果对这种情况有任何了解，我将不胜感激:

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);
}

Answer 1

基本上，您是在问这三者之间的区别:

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，因为您正在将一个全新的对象分配给this.name。这个新对象 ({'t2':"m2"}) 与 this.message 完全无关。

也许您正在尝试/想做的是:

this.name.t2 = "m2";

它与 #2 和 #3 相同，影响 this.message，因为 this.name 仍然 指的是同一个对象.

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

Object.assign(this.name, {'t2':"m2"});